Exit trap cleanup in docstheme-build-translated.sh
Exit trap cleanup in docstheme-build-translated.sh

Add a catch-all `cleanup` exit trap to docstheme-build-translated.sh.
The script creates interim artifacts in doc/source (which it arguably
shouldn't do) like .pot files and .rst sources modified with index
headers pointing to translations. Previously, if the doc build failed,
these artifacts would be left behind, creating a mess for a developer
attempting to make and commit doc changes locally. This patch
accumulates the existing cleanups into an exit trap so they happen
whether the script succeeds or fails.

Developers of openstackdocstheme itself may disable this cleanup trap by
setting the DOCSTHEME_BUILD_TRANSLATED__NO_CLEANUP environment variable
to a nonempty value.

Change-Id: If48c5705c34f940e78e3a34e602e48496a397629

openstack/openstackdocstheme,openstack/openstackdocstheme,openstack/openstackdocstheme,openstack/openstackdocstheme