[CloneProfile] Create user mount directory before creating bind mounts.

In aosp/2679182 the capability to add bind mounts for clone user
in public volumes was added.
This allows apps in clone profile to access public volume via lower
fs.
However, sometimes, the user mount directory (/user/mount/<user-id>)
is itself not present, resulting in failures of public volume
bind mounts. This CL addresses this.

Bug: 327293687
Test: Manul build and flash
Change-Id: I0680a518cb14983c6f2e636a38ab6dcd476d7eab
4 files changed