Remove unused OS_TEST_TIMEOUT variable
Remove unused OS_TEST_TIMEOUT variable

When running the unit tests, this environment variable was being
set: OS_TEST_TIMEOUT=60. However, this variable isn't used, and
there doesn't seem to be a need to use it, so it is removed here.

Change-Id: Iede6fda9f8844ec1769ec988eade9229f55521c6

openstack/python-ironicclient,rdo-management/python-ironicclient,NaohiroTamura/python-ironicclient,openstack/python-ironicclient,NaohiroTamura/python-ironicclient,bcrochet/python-ironicclient