Squash UMS Commits [2/3]

Credits: CyanogenMod

Change-Id: Ieb2a7c0e125c7ca7a5751a2ebd1c02eb92cef2bb
vold: Allow ASEC containers on an external volume when internal is emulated

Thanks to Pierre-Hugues Husson for the idea in this patch! The initial
implementation called createBindMounts() on all mount points regardless
of whether or not it was the SD card.

Change-Id: Ic2c45d275179099065a10e1e664a08efea66acf1