db-ctl-base: Don't die in is_condition_satisfied() on error.

db-ctl-base: Don't die in is_condition_satisfied() on error.

Return the error message to the caller instead of reporting it and dying
so that the caller can handle the error without terminating the process
if needed.

Also, rename the function as it is no longer a typical predicate, so
that the users don't assume that the result is passed in return value.

Signed-off-by: Jakub Sitnicki <jkbs@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>