Kick movement preconditions onto handler thread.

The bulk of package moving already occurs on the handler thread,
but one of the precondition steps requires that we make an installd
call to calculate disk space of the app.  If there was already
another long-running installd call going on, we could end up ANR'ing
the caller.

Since movePackage() is already designed to return a moveId and go
async, we can push all the precondition steps onto the handler thread
to prevent the ANR.

Bug: 25490003
Change-Id: I62d555c23bbf81b791f6f4cabc40c3d64c580cf8