Protect /mnt/scratch from stale umount on userdebug

On userdebug protect /mnt/scratch. On user builds ensure that
/mnt/scratch is considered a stale mount so it can not be used.
vold runs before ro.debuggable is set, so this must be a compile
time decision.

Minor technical debt cleanup associated with using android::base.

Test: compile
Bug: 109821005
Change-Id: I8efdbedfe850dd24daecf03a37aea61de47edc7d
2 files changed