vold: allow override of MAX_PARTITIONS for devices with > 32 partitions

Default was updated to 32 and the error messages were changed to be less cryptic.

(cherry picked from commit cb80fef89874cb2833f93e7c6f0da214467e96b8)

Change-Id: I244f48c576af05b6569c8c40ebeb4ed1bfa53469