remount: Check device mapper to see if verity is already disabled

No matter verity is enabled or disabled, androidboot.veritymode is
always "enforcing" on emulator kernel cmdline.

This is a violation of the AVB contract:
https://cs.android.com/android/platform/superproject/+/master:external/avb/README.md#handling-dm-verity-errors

Before emulator can fix this, workaround this by checking the device
mapper table to see if verity is disabled or not.
If no "<partition>-verity" device is present, than assume verity is
already disabled.

Also log mountpoints that are successfully remounted.

Bug: 241688845
Bug: 259207493
Test: adb-remount-test
Test: Run adb remount on emulator
Change-Id: Id5767b05cbfb48adf2a8c372dfdad4d15b98e091