When requested, kick off a thread that will migrate storage contents
between two locations. This is performed in several steps that
also interact with the framework:
1. Take old and new volumes offline during migration
2. Wipe new location clean (10% of progress)
3. Copy files from old to new (60% of progress)
4. Inform framework that move was successful so it can persist
5. Wipe old location clean (15% of progress)
Derives a hacky progress estimate by using a rough proxy of free
disk space changes while a cp/rm is taking place.
Add new internal path for direct access to volumes to bypass any
FUSE emulation overhead, and send it to framework. Remove mutex
around various exec calls since setexeccon() is already per-thread.
Bug: 19993667
Change-Id: Ibcb4f6fe0126d05b2365f316f53e71dc3e79a2b8
