Move test_waiters to match directory structure

This simply makes the test_waiters module mimic the source
location for tempest/common/waiters so that goofballs such as
myself don't try to create a new test module to add new tests.

Change-Id: Ic82f05f6c3032f7412dc9a588112815d6df1db22
diff --git a/tempest/tests/test_waiters.py b/tempest/tests/common/test_waiters.py
similarity index 100%
rename from tempest/tests/test_waiters.py
rename to tempest/tests/common/test_waiters.py