Support Zygote mounting FUSE mount paths while forking

If the persist.sys.fuse flag is true, Zygote will mount
/mnt/user/<userid> on /storage. This will effectively provide
/storage/self/primary symlinked to /storage/emulated/<userid>
This will allow apps access FUSE instead of sdcardfs on /sdcard

If the persist.sys.fuse flag is false (the default). No behavior changes

Bug: 135341433
Test: m && device boots successfully && seems to work ok
Change-Id: If5ee53cc4c18e52481f670be001c581b7f520343