Remove "nova-manage flavor list" CLI test

The "nova-manage flavor" sub-commands were deprecated in Juno and Nova
change I1798c8a0697009b3dcebeb818580c8323880e395 removes them.

This removes the test_flavor_list test and changes the test_debug_flag
and test_verbose_flag tests to use 'nova-manage service list' instead of
'nova-manage flavor list'.

Change-Id: I4e2399f2fbab2c20299dd62c104b9220c1d36fb2
diff --git a/tempest/cli/simple_read_only/compute/test_nova_manage.py b/tempest/cli/simple_read_only/compute/test_nova_manage.py
index c27b12e..a4c7aa1 100644
--- a/tempest/cli/simple_read_only/compute/test_nova_manage.py
+++ b/tempest/cli/simple_read_only/compute/test_nova_manage.py
@@ -65,20 +65,17 @@
                          self.nova_manage('', '--version', merge_stderr=True))
 
     def test_debug_flag(self):
-        self.assertNotEqual("", self.nova_manage('flavor list',
+        self.assertNotEqual("", self.nova_manage('service list',
                             '--debug'))
 
     def test_verbose_flag(self):
-        self.assertNotEqual("", self.nova_manage('flavor list',
+        self.assertNotEqual("", self.nova_manage('service list',
                             '--verbose'))
 
     # test actions
     def test_version(self):
         self.assertNotEqual("", self.nova_manage('version'))
 
-    def test_flavor_list(self):
-        self.assertNotEqual("", self.nova_manage('flavor list'))
-
     def test_db_sync(self):
         # make sure command doesn't error out
         self.nova_manage('db sync')