Add replace_address_first_boot flag to only replace if not bootstrapped.

Patch by brandonwilliams, reviewed by thobbs for CASSANDRA-7356
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	CHANGES.txt
Merge branch 'cassandra-2.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk