Manually unmount /data_mirror mounts in the right order

Test: atest CtsUserspaceRebootHostSideTestCases
Bug: 152823078
Change-Id: I57ff9182807630d8cbcf3ca6374fdd6dc6379da5
Merged-In: I57ff9182807630d8cbcf3ca6374fdd6dc6379da5
(cherry picked from commit bf66f433d6b43322dc73bc1160ce542a7705ce00)
1 file changed