On some devices, having the vendor partition mounted
causes slot switching to fail ("Error getting bootctrl module")
Automatically unmount vendor partition prior to switching
slots to ensure the process completes successfully.
Use lazy unmount if Unmount_by_Path function fails.
TEST: Mount vendor partition, then switch slots.
Vendor partition should be unmounted when
switching completes
Change-Id: If6198d4693141be464749c4d423a9088753d939e
b60a2732d5