Do not suppress severe exception when password change fails

Redefine the return condition of LPU.saveLock{Password,Pattern}:

1. When password change fails due to the caller providing an
incorrect existing password (or password throttling is still
being enforced), treat this as a normal failure mode and return
false.
2. For all other exceptions thrown during password change,
throw it to the caller so it fails fast, instead of relying
on the caller to check the return value.

Bug: 62410009
Test: atest com.android.server.locksettings
Change-Id: I8fa6320b7134d18ed5dae1af7f6f05002100d291