COIL: Add unblocked_terms.txt to block keywords

Currently the global unblocked_terms.txt are in effect. Since
it's identical to the global blocked_terms.txt, nothing is being
blocked.

This patch adds unblocked_terms.txt, which overrides the global one.

BUG=b:165908442, b:163885307
BRANCH=none
TEST=repo upload --cbr --dry-run .

Cq-Depend: chromium:2369239
Signed-off-by: Daisuke Nojiri <[email protected]>
Change-Id: Ib4c70c7e210781309fe66fbb00569673eff0fb0f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2369353
Reviewed-by: Paul Fagerburg <[email protected]>

Author: dnojiri

unblocked_terms.txt

@@ -0,0 +1,2 @@
+master
+slave