make sure KEYWORDS are set correctly in ebuilds

We want to get people to start using KEYWORDS=* to mark their ebuilds
stable, so add a hook to catch that.

BUG=chromium:307180
TEST=tried uploading files with various KEYWORDS and saw pass/fail as needed:
	accepted:
		KEYWORDS=
		KEYWORDS=""
		KEYWORDS="*"
		KEYWORDS="~*"
		KEYWORDS="-*"
		KEYWORDS="-* arm"
	rejected:
		KEYWORDS="arm"
		KEYWORDS="~arm"
		KEYWORDS="amd64 arm x86"

Change-Id: I5f3a8071b22bc3f1c0b14ce26ecd6ec2b00e183a
Reviewed-on: https://chromium-review.googlesource.com/183650
Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
1 file changed