Add more mounting options to updater mount function.

If enabling the oem partition, it will be mounted by updater before
reading product properties from it. To be safety, we want to enable AVB
to this oem partition. But this means the oem partition can never be
mounted to writable. Otherwise, that partition will be corrupted to AVB
verifying.
This change follows fs_mgr to allow to pass more mounting options to the
updater.

BUG: 150156957
Test: make ota package which mounts AVB oem partition to read only and
run OTA.

Change-Id: I2ebbe3c8ac53c70112f3fed2703fcba9170405a6