Isolate change_server_password to use its own server

If this test is being run with others, it will mess up tests ahead
of it by changing the admin password of the instance.  Solving this
by creating a new server just for this test.

Change-Id: Id2c4fadd096db3d403a669139fe3caea98628c6b
Closes-Bug: #1632118
diff --git a/tempest/api/compute/servers/test_server_actions.py b/tempest/api/compute/servers/test_server_actions.py
index 28ee739..788dd8a 100644
--- a/tempest/api/compute/servers/test_server_actions.py
+++ b/tempest/api/compute/servers/test_server_actions.py
@@ -81,14 +81,19 @@
     @testtools.skipUnless(CONF.compute_feature_enabled.change_password,
                           'Change password not available.')
     def test_change_server_password(self):
+        # Since this test messes with the password and makes the
+        # server unreachable, it should create its own server
+        newserver = self.create_test_server(
+            validatable=True,
+            wait_until='ACTIVE')
         # The server's password should be set to the provided password
         new_password = 'Newpass1234'
-        self.client.change_password(self.server_id, adminPass=new_password)
-        waiters.wait_for_server_status(self.client, self.server_id, 'ACTIVE')
+        self.client.change_password(newserver['id'], adminPass=new_password)
+        waiters.wait_for_server_status(self.client, newserver['id'], 'ACTIVE')
 
         if CONF.validation.run_validation:
             # Verify that the user can authenticate with the new password
-            server = self.client.show_server(self.server_id)['server']
+            server = self.client.show_server(newserver['id'])['server']
             linux_client = remote_client.RemoteClient(
                 self.get_server_ip(server),
                 self.ssh_user,