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

Conflicts:
	VolumeManager.cpp
Merge branch 'cm-11.0' of https://github.com/temasek/android_system_vold into HEAD

Conflicts:
	Android.mk

Change-Id: Iae8f79914784e146311b8e848c0f5985d7119a47