make INSTALLED_BUILD_PROP_TARGET A BIG FAT PHONY

Change-Id: I46fd001e4237753d870edf964dc414419661dc33
Other roms don't have these... and they're the same for every cpu anyways

Change-Id: I4f1cb7eacb293115a86944704ae264955addd813
add multiple key support to signapk

Support signing .apks (but not OTA packages) with multiple keys.

Bug: 7350459
Change-Id: I794e1da0555e2bb9247a59c756656d4ca7ee04cf