handle jarsigner/apksigner output cleanly for rational logging

These were both spamming the output with lots of confusing messages, even
when --verbose was not used.  Jarsigner especially has confusing messages,
since it has warnings that do not pertain to APK signatures at all, like
the ones about timestamps and missing Certificate Authority.

closes #405
2 jobs for rational-jarsigner-logging in 25 minutes and 8 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #43628357
metadata_v0

00:03:55

passed #43628356
test

00:25:08