installd: Check for support before migrating obb

This prevents migrating the obb folder if the device's kernel does not
support the new location.

Test: Run script on kernel with support for the unshared_obb option, and
      without, i.e. P kernel and Q kernel
Bug: 136199978

Change-Id: I3ff3e7653d9c9c6cdda4d17bafc853b5602597cf