build: Ensure /system unmounted at install start Account for the possibility that a user has mounted system manually before installing the FullOTA package.
build: Ensure /system unmounted at install start
Account for the possibility that a user has mounted system manually
before installing the FullOTA package.

Change-Id: I2c256765132a5296eff320e66a1703b2d9bcac98

xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build,xorware/android_build