Add config fixture support to unit tests

This commit adds a new env variable OS_TEST_LOCK_PATH to the
.testr.conf file to set the lock path for using oslo locks.
Previously, if an external lock couldn't be used to isolate test cases
because the unit tests do not have a config file. By getting a lock
path with an env variable and setting the location in the config
fixture external locks can be used by first invoking the config
fixture.

Partially implements bp unit-tests

Change-Id: I08c27ab125183f5d055eaa45c4f0e0a527445475
diff --git a/.testr.conf b/.testr.conf
index abaf14a..4f6e0b3 100644
--- a/.testr.conf
+++ b/.testr.conf
@@ -2,6 +2,7 @@
 test_command=OS_STDOUT_CAPTURE=${OS_STDOUT_CAPTURE:-1} \
              OS_STDERR_CAPTURE=${OS_STDERR_CAPTURE:-1} \
              OS_TEST_TIMEOUT=${OS_TEST_TIMEOUT:-500} \
+             OS_TEST_LOCK_PATH=${OS_TEST_LOCK_PATH:-${TMPDIR:-'/tmp'}} \
              ${PYTHON:-python} -m subunit.run discover -t ./ ${OS_TEST_PATH:-./tempest/test_discover} $LISTOPT $IDOPTION
 test_id_option=--load-list $IDFILE
 test_list_option=--list