add equery-$board autocomplete

After starting down the programmatic autocomplete garden path, I
realized that the equery autocomplete did not cover all the
equery-$board use cases which are probably even more common, so I
couldn't resist adding those as well.

BUG=None
TEST=after calling setup_board for some particular $board,
`equery-$board [tab][tab]` will show autocomplete list of equery
commands.

Change-Id: I007e8a4867c08b6585fb90174f34ced73b73aedd
Reviewed-on: https://gerrit.chromium.org/gerrit/45531
Tested-by: Aviv Keshet <akeshet@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Aviv Keshet <akeshet@chromium.org>
1 file changed