Deal with MediaProvider process dying.

There is no way to recover the FUSE filesystem once the MediaProvider
process has died; the kernel and userspace are out of sync at that
point, and libfuse will return -EIO on all requests.

Now when the process dies, tell StoragemanagerService that it needs to
reset all volumes for a user. Since we currently don't have a way to do
this for one user, just call through to H_RESET. This can be optimized
later. This also means we no longer need to keep a hold of the FUSE fd
in system_server; just pass it along directly when we start a session.

Bug: 137890172
Test: atest AdoptableHostTest
Change-Id: I2e6952ccece6bf2945b4ed81c70330b278554d13