vold: dont't use commas in device names

Fuse supports commas escaped by '\' in fs names, but exfat and ntfs-3g
currently don't support the escaping.

This fixes mounting of exFAT and NTFS public volumes.

Change-Id: I72005489956e59e7f889267114fee3921d289984

Also change emulated device id separator from comma to underscore

Needed to fix emulated primary storage on adopted storage.

Change-Id: I22114698e480fc829090261b79824c8b65b009c3
4 files changed