This allows subparsers more control over which sets of arguments they need to
implement. For example, it doesn't make sense for the 'empty' selector to
accept the preset arguments. Now it can opt-out of those and only implement
the 'push' arguments.
MozReview-Commit-ID: GOfjcFtlfDD
This adds all the common arguments to |mach try empty|, including preset
arguments which will just be ignored if specified. The commit message can be
changed with:
./mach try empty -m DONTBUILD
MozReview-Commit-ID: 5RYfLBOIX1g
