Use a single thread to handle multiple AppFuse mounts.

Previously StorageManagerService launched a thread per AppFuse mount
point. The CL changes the behavior so that it just launches a single
thread to handle multiple AppFuse mounts.

Bug: 34903085
Test: CTS and manually testing
Change-Id: I2d9e7232834b0c8eff633b85110a3b38534171f7
3 files changed