reprioritize gate and check queues

Bump check queue to normal priority so that it will get resources
before merge-check or silent queues. Same for triple-o check, for same
reasons.

Bump gate queue to high priority to keep it ahead of the check
queue. It was brought back down to normal previously because it was
starving release jobs, however with the new sliding window on the gate
we effectively cap gate capacity, and this shouldn't be an actual
issue.

Change-Id: I7430c7293ad843a405d321d987c9dfaf7b4ab364