Don't split up valid boolean expressions as parameters.

Parallel of this commit in genome:
commit 3614eeadd2f75a232d02a1787bafc79afe27048a

This would lead to, e.g., run_by=apipe-tester,status=Unstartable returning
the set of all apipe-tester builds when none are unstartable... which is
unexpected.

run_by=apipe-tester,run_by=apipe-builder should still translate to an "or".