if reset fails, display the command that failed

we get failures in _reset_databases from time to time, and it's
hard to debug without understanding what command failed. Make
this show up in the assert message.

Now with even more output!

Change-Id: Ie82109cfb1745e7218e0906764db1fad0c8fc5f5
Merge "if reset fails, display the command that failed"
Merge remote-tracking branch 'm_src_repo/master' into build-temp