Don't touch info_cache after refreshing it in Instance.refresh()

We were touching info_cache to force it to be marked dirty in the
instance object after refreshing it. However, it isn't dirty, because
it has just been refreshed and the relationship to instance hasn't
been altered. Also, the dirty state on the instance object is
unconditionally reset immediately after this anyway.

Change-Id: Ibc8e9d95210d14c946f6f820492da2331c0d7fab
Merge "Don't touch info_cache after refreshing it in Instance.refresh()"