cuttlestone: rename busytown script to match full target name

This brings the name of the busytown script in line with all other
instances of the name of this target (lunch & overlay configuration).
This is also the same as all of the other Keystone busytown targets.

Bug: 112754932
Change-Id: I8959d3a74b8f7b5dc69a17e1071724301a07803d