Added HIDL based software implementation of gatekeeper

This patch adds a HIDL based software implementation of gatekeeper based
on libgatekeeper.

Also adds OWNER files to the vts test and default implementation
directories.

Test: Manually tested in emulator. Changing passwords and login worked.
      VtsHalGatekeeperV1_0TargetTest
      gatekeeper-software-device-unit-tests
Change-Id: I632aeb6677640c133ec1b79e72568840adbc0550
Merged-In: I632aeb6677640c133ec1b79e72568840adbc0550