Additional checks to prevent partitioning internal storage

Change-Id: I9fcd7e0169fbdd52405c0c86aafbef091f69411e
Merge branch 'android-4.4' of github.com:omnirom/android_bootable_recovery
multirom: updates to support installing to external SD
Merge pull request #4 from CaptainThrowback/master

multirom: updates to support installing to external SD
Merge remote-tracking branch 'Tasssadar/master'