Fix get_versions string parsing

During the recent rest client refactor the _parse_resp() method was
improved to detect whether there was a single key at the top level
and drop it if there was. However the get_versions() method wasn't
updated at the same time, this led to the 'versions' being
referenced when it was removed from the resp dict. This commit fixes
this by removing the reference to versions.

Change-Id: I92003bd3f8c63a61a0d078d141e86dea4115bb80
Merge "Fix get_versions string parsing"