Rename test_resources to test_instance

Since that's what it's actually testing.

Change-Id: I03556778587e4b1b3a38bf755137eef08455e8f3
Signed-off-by: Zane Bitter <zbitter@redhat.com>

diff --git a/heat/tests/test_resources.py b/heat/tests/test_instance.py
similarity index 100%
rename from heat/tests/test_resources.py
rename to heat/tests/test_instance.py