Do not mount storage obb&data dirs in fuse daemon process

Otherwise, fuse daemon will be killed during storage dir remount.
Also, fix wrong uid in prepareObbDirs() for multi-user case.

Bug: 151452792
Bug: 151436460
Test: atest AdoptableHostTest
Change-Id: Ib0d4cba36bc1bc91f31583c6a97d37203ac8b88d