Only show ART information if switching from dalvik to ART

We do not want to confuse users with a big information dialog, if
they change from ART to dalvik as dalvik is still the official
solution, supported and considered safe.

Change-Id: I0ce4846e0bb751e87e5c410e668d4bc521380141
Merge "Only show ART information if switching from dalvik to ART" into cm-11.0