Deprecate BaseTempestTestCase.create_and_associate_floatingip method

Add new 'debtcollector' dependency with the purpose of deprecating methods
that are going to be removed.

Mark BaseTempestTestCase.create_and_associate_floatingip for removal.

Replace create_and_associate_floatingip with create_floatingip in
BaseTempestTestCase class.

Change-Id: I5c5fd143a5cb4e138c46d13445f8225444bd2f58
diff --git a/requirements.txt b/requirements.txt
index 5660c68..e48daf7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -16,3 +16,4 @@
 testtools>=2.2.0 # MIT
 testscenarios>=0.4 # Apache-2.0/BSD
 eventlet!=0.18.3,!=0.20.1,>=0.18.2 # MIT
+debtcollector>=1.2.0 # Apache-2.0