Move test decorators to common

services and extension decorators are based on CONF and needed by
Tempest only, so moving them to tempest.common.
Since a few plugnis use them today, use debtcollector to avoid
breaking all dependencies.

Change-Id: Ibd52153d00b8e60fb8c89e38d94e358ddc787251
diff --git a/HACKING.rst b/HACKING.rst
index 446d865..cb9821e 100644
--- a/HACKING.rst
+++ b/HACKING.rst
@@ -358,10 +358,10 @@
 
 When adding tests for new features that were not in previous releases of the
 projects the new test has to be properly skipped with a feature flag. Whether
-this is just as simple as using the @test.requires_ext() decorator to check
-if the required extension (or discoverable optional API) is enabled or adding
-a new config option to the appropriate section. If there isn't a method of
-selecting the new **feature** from the config file then there won't be a
+this is just as simple as using the @utils.requires_ext() decorator to
+check if the required extension (or discoverable optional API) is enabled or
+adding a new config option to the appropriate section. If there isn't a method
+of selecting the new **feature** from the config file then there won't be a
 mechanism to disable the test with older stable releases and the new test won't
 be able to merge.