Switch to socket communication with uncrypt.

RecoverySystemService used to communicate with uncrypt via files (e.g.
/cache/recovery/command and /cache/recovery/uncrypt_status). Since A/B
devices may not have /cache partitions anymore, we switch to communicate
via /dev/socket/uncrypt to allow things like factory reset to keep
working.

Bug: 27176738
Change-Id: I109aa9a9592ca6074eb210089963a846955c0768