cros_workon_make: support passing through env vars to the ebuild

When doing iterative work, you often want to build just one or two
things first before falling back to a full build.  Support passing
through env vars so we can do that.

BUG=chromium:311351
TEST=`cros_workon_make --board x86-generic crash-reporter` still works

Change-Id: I0ec5110fc2f432b8d83e26d7265edbc20c5a104a
Reviewed-on: https://chromium-review.googlesource.com/174677
Reviewed-by: Chris Sosa <sosa@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
1 file changed