authpolicy: Clean state on startup

Cleans state on startup when install attributes are not set to Active
Directory enrollment. This might occur if something unexpected happens
during enrollment, e.g. the user cancels domain join.

Also cleans up AuthPolicy construction and simplifies ownership of
metrics and paths, which makes some *ForTesting accessors obsolete.

BUG=chromium:713754
TEST=Compiled, ran tests, tested on device.

Change-Id: If1cf6c406c75423d1900d460e9200737a800730e
Reviewed-on: https://chromium-review.googlesource.com/485601
Commit-Ready: Lutz Justen <ljusten@chromium.org>
Tested-by: Lutz Justen <ljusten@chromium.org>
Reviewed-by: Thiemo Nagel <tnagel@chromium.org>
6 files changed