Change message in FailuresQueryParamsSerializer (#3967)
Change message in FailuresQueryParamsSerializer (#3967)

clarify error message in validate_bug since a bug can exist in bugzilla
but not exist in our bugscache if its not an intermittent failure
KWierso/treeherder,edmorley/treeherder,edmorley/treeherder,edmorley/treeherder,KWierso/treeherder,KWierso/treeherder,KWierso/treeherder,edmorley/treeherder