apman: ignore non-sense files.

Temporary files, files left over from development versions of the code,
and the like could confuse apman and cause it to either fail to start
APs, or start APs and then immediately stop them.

These bugs were latent for some time, but became apparent after we
stopped persisting portal APs.

Fixes b/32702329.

Change-Id: Id18502cdc69a7735e586326e0507e35070f65644
2 files changed