Deprecate resources_prefix and change rand_name()

Many projects are using rand_name() which is outside of tempest.lib.
The method specifies the prefix 'tempest', which is the default value
of tempest.conf, to tempest.lib's rand_name().
The prefix is useful to identify these resources are created by Tempest.
No projects change this configuration value, so this patch changes the
default value of rand_name() to 'tempest' and makes resources_prefix
option deprecated.

Change-Id: I624e2eb3954b6171fbbe00a4ed757bfac04b3eaf

releasenotes/notes/deprecate-resources-prefix-option-ad490c0a30a0266b.yaml

@@ -0,0 +1,10 @@
+---
+upgrade:
+  - The default value of rand_name()'s prefix argument is changed
+    to 'tempest' from None to identify resources are created by
+    Tempest.
+deprecations:
+  - The resources_prefix is marked as deprecated because it is
+    enough to set 'tempest' as the prefix on rand_name() to
+    ideintify resources which are created by Tempest and no
+    projects set this option on OpenStack dev community.

tempest/config.py

@@ -1021,7 +1021,12 @@ DefaultGroup = [
                help="Prefix to be added when generating the name for "
                     "test resources. It can be used to discover all "
                     "resources associated with a specific test run when "
-                    "running tempest on a real-life cloud"),
+                    "running tempest on a real-life cloud",
+               deprecated_for_removal=True,
+               deprecated_reason="It is enough to add 'tempest' as this "
+                                 "prefix to ideintify resources which are "
+                                 "created by Tempest and no projects set "
+                                 "this option on OpenStack dev community."),
 ]
 
 _opts = [

tempest/lib/common/utils/data_utils.py

@@ -43,7 +43,7 @@ def rand_uuid_hex():
     return uuid.uuid4().hex
 
 
-def rand_name(name='', prefix=None):
+def rand_name(name='', prefix='tempest'):
     """Generate a random name that includes a random number
 
     :param str name: The name that you want to include

tempest/tests/lib/common/utils/test_data_utils.py

@@ -37,16 +37,20 @@ class TestDataUtils(base.TestCase):
         actual2 = data_utils.rand_uuid_hex()
         self.assertNotEqual(actual, actual2)
 
-    def test_rand_name(self):
-        actual = data_utils.rand_name()
+    def test_rand_name_with_default_prefix(self):
+        actual = data_utils.rand_name('foo')
         self.assertIsInstance(actual, str)
-        actual2 = data_utils.rand_name()
+        self.assertTrue(actual.startswith('tempest-foo'))
+        actual2 = data_utils.rand_name('foo')
+        self.assertTrue(actual2.startswith('tempest-foo'))
         self.assertNotEqual(actual, actual2)
 
-        actual = data_utils.rand_name('foo')
-        self.assertTrue(actual.startswith('foo'))
-        actual2 = data_utils.rand_name('foo')
+    def test_rand_name_with_none_prefix(self):
+        actual = data_utils.rand_name('foo', prefix=None)
+        self.assertIsInstance(actual, str)
         self.assertTrue(actual.startswith('foo'))
+        actual2 = data_utils.rand_name('foo', prefix=None)
+        self.assertTrue(actual2.startswith('foo'))
         self.assertNotEqual(actual, actual2)
 
     def test_rand_name_with_prefix(self):