If a plugin is symlinked in the plugins folder, and that plugin does
not have any tags, the `git describe` command fails with:
fatal: No names found, cannot describe anything
which causes the build to fail. This was broken by change If5e7be8d.
Add the `--always` option on `git describe` so that it will return a
value even when there are no tags.
Change-Id: I3d0c472c9ac469d079626a9df17149422dc5e4e6