I just did this! /data/property/persist.sys.dalvik.vm.lib
/data/property/persist.sys.dalvik.vm.lib
is a textfile containing one of two values: 'libart.so' or 'libdvm.so'. You can change from ART to Dalvik simply by editing this file.
Ex: adb shell 'echo libdvm.so >/data/property/persist.sys.dalvik.vm.lib'