Provide secret to vold to remove credential

vold requires the secret to retrieve the CE key
to re-wrap without auth when the user removes
the credential.

Test: Set credential, remove credential, swipe to none
and vice-versa.
Unit tests under locksettings

Bug: 26948053
Merged-In: I14503404ddd330cced2f2ff0e8f500cbe3f96e28
Change-Id: I14503404ddd330cced2f2ff0e8f500cbe3f96e28
5 files changed