The CL:
* Adds StorageManager#openProxyFileDescriptor API.
* Turns IProxyFileDescriptorCallback into a class so that it can provides
default implementations.
* Removes mActive state from FuseAppLoop, because the state will be managed at
the MountService side.
* Adds StorageManagerIntegrationTest to check if FUSE is correctly mounted or
not. Since it's implementation details, CTS does not help to test the
behavior.
Test: StorageManagerIntegrationTest
Bug: 29970149
Change-Id: Id78dd4abcf9325820e9c77c264f54bfa77b85a92
9fb00183a0