Fix test_attach_detach_volume test case to not rely on user/libvirt supplied disk name

This patch removes user provided and libvirt assigned
value as that was based on assumption rather count the
disk name before and after attach/detach based on output
generated using 'lsblk' command  in the running instance
with the help of new method list_disks in client and
existing util remote client for remote ssh.

we observer this test case failing when the instance boot
with config drive format "vfat" enabled with two volume
vda and vdb volume disk name, so whatever test case boot with
config drive as well as ephemeral disk  was not be able to
use this testcase.

Change-Id: Id3e537bc55089ca5c35fa1f973dd47f2b11147ae
Partial-Bug: #1852807
diff --git a/tempest/api/compute/volumes/test_attach_volume.py b/tempest/api/compute/volumes/test_attach_volume.py
index f83e62c..92524fc 100644
--- a/tempest/api/compute/volumes/test_attach_volume.py
+++ b/tempest/api/compute/volumes/test_attach_volume.py
@@ -41,11 +41,6 @@
         cls.prepare_instance_network()
         super(BaseAttachVolumeTest, cls).setup_credentials()
 
-    @classmethod
-    def resource_setup(cls):
-        super(BaseAttachVolumeTest, cls).resource_setup()
-        cls.device = CONF.compute.volume_device_name
-
     def _create_server(self):
         # Start a server and wait for it to become ready
         validation_resources = self.get_test_validation_resources(
@@ -84,15 +79,18 @@
             # NOTE(andreaf) We need to ensure the ssh key has been
             # injected in the guest before we power cycle
             linux_client.validate_authentication()
+            disks_before_attach = linux_client.count_disks()
 
         volume = self.create_volume()
 
         # NOTE: As of the 12.0.0 Liberty release, the Nova libvirt driver
-        # no longer honors a user-supplied device name, in that case
-        # CONF.compute.volume_device_name must be set the equal value as
-        # the libvirt auto-assigned one
-        attachment = self.attach_volume(server, volume,
-                                        device=('/dev/%s' % self.device))
+        # no longer honors a user-supplied device name, and there can be
+        # a mismatch between libvirt provide disk name and actual disk name
+        # on instance, hence we no longer validate this test with the supplied
+        # device name rather we count number of disk before attach
+        # detach to validate the testcase.
+
+        attachment = self.attach_volume(server, volume)
 
         self.servers_client.stop_server(server['id'])
         waiters.wait_for_server_status(self.servers_client, server['id'],
@@ -103,9 +101,8 @@
                                        'ACTIVE')
 
         if CONF.validation.run_validation:
-            disks = linux_client.get_disks()
-            device_name_to_match = '\n' + self.device + ' '
-            self.assertIn(device_name_to_match, disks)
+            disks_after_attach = linux_client.count_disks()
+            self.assertGreater(disks_after_attach, disks_before_attach)
 
         self.servers_client.detach_volume(server['id'], attachment['volumeId'])
         waiters.wait_for_volume_resource_status(
@@ -120,8 +117,8 @@
                                        'ACTIVE')
 
         if CONF.validation.run_validation:
-            disks = linux_client.get_disks()
-            self.assertNotIn(device_name_to_match, disks)
+            disks_after_detach = linux_client.count_disks()
+            self.assertEqual(disks_before_attach, disks_after_detach)
 
     @decorators.idempotent_id('7fa563fe-f0f7-43eb-9e22-a1ece036b513')
     def test_list_get_volume_attachments(self):
diff --git a/tempest/common/utils/linux/remote_client.py b/tempest/common/utils/linux/remote_client.py
index dad710c..5875da3 100644
--- a/tempest/common/utils/linux/remote_client.py
+++ b/tempest/common/utils/linux/remote_client.py
@@ -73,6 +73,13 @@
             msg = "'TYPE' column is required but the output doesn't have it: "
             raise tempest.lib.exceptions.TempestException(msg + output)
 
+    def count_disks(self):
+        disks_list = self.get_disks()
+        disks_list = [line[0] for line in
+                      [device_name.split()
+                       for device_name in disks_list.splitlines()][1:]]
+        return len(disks_list)
+
     def get_boot_time(self):
         cmd = 'cut -f1 -d. /proc/uptime'
         boot_secs = self.exec_command(cmd)
diff --git a/tempest/tests/common/utils/linux/test_remote_client.py b/tempest/tests/common/utils/linux/test_remote_client.py
index 644a018..caad41c 100644
--- a/tempest/tests/common/utils/linux/test_remote_client.py
+++ b/tempest/tests/common/utils/linux/test_remote_client.py
@@ -106,6 +106,15 @@
         self.assertEqual(self.conn.get_disks(), result)
         self._assert_exec_called_with('lsblk -lb --nodeps')
 
+    def test_count_disk(self):
+        output_lsblk = """\
+NAME       MAJ:MIN    RM          SIZE RO TYPE MOUNTPOINT
+sda          8:0       0  128035676160  0 disk
+sdb          8:16      0 1000204886016  0 disk
+sr0         11:0       1    1073741312  0 rom"""
+        self.ssh_mock.mock.exec_command.return_value = output_lsblk
+        self.assertEqual(self.conn.count_disks(), 2)
+
     def test_get_boot_time(self):
         booted_at = 10000
         uptime_sec = 5000.02