devstack fails with trema when execute
"sudo a2ensite sliceable_switch" command, without ".conf" filename extension
with Apache2.4, Apache2.22. With Apache 2.2, it successes.
Because in the versions which newer than version 2.2,
file checking of a2ensite command is more severe.
So, a2ensite command forbid "sliceable_switch" without "/conf".
Added ".conf" filename extension.
Change-Id: I29a03cb59ee493345b7df0f1a9189eb3516c86e2
Closes-Bug: #1263017