vold will store password securely until KeyGuard requests it
and hands it on to KeyStore.
This is a revision of
https://googleplex-android-review.git.corp.google.com/#/c/418123/
which was reverted. It had two bugs in LockSettingsService.checkVoldPassword.
1) We were not checking password for null, which caused an exception
2) checkPattern/checkPassword return true if there is no saved pattern or password.
This leads to situations where we get true returned even when the password
doesn't match. Call the correct one based on what is there, not what vold
thinks ought to be there.
Bug: 12990752
Change-Id: I05315753387b1e508de5aa79b5a68ad7315791d4
945490c12e