SSP doesn't cache seeds forever

Patch by brandonwilliams, reviewed by jbellis for CASSANDRA-7663
Remove shuffle/taketoken

Patch by brandonwilliams, reviewed by thobbs for CASSANDRA-7601
Set gc_grace_seconds to 7 days for system schema tables

Patch by Tyler Hobbs; review by Aleksey Yeschenko for CASSANDRA-7668
Support connecting to ipv6 jmx with nodetool
patch by Robert Stupp; reviewed by jbellis for CASSANDRA-7669
remove shuffle bat again
Prevent SSP from erroring out when the yaml is yanked from it.

Patch by brandonwilliams, reviewed by Richard Low for CASSANDRA-7663
Add stop method to EmbeddedCassandraService

patch by lyubent; reviewed by slebresne for CASSANDRA-7595
Fix test/system/test_thrift_server.py
Fix more of test/system/test_thrift_server.py
Clone token map outside of hot gossip loops
patch by rbranson; reviewed by jbellis for CASSANDRA-7758
Remove duplicates from StorageService.getJoiningNodes
patch by jbellis; reviewed by ayeschenko for CASSANDRA-7478
Fix race in background compaction check

patch by yukim; reviewed by krummas for CASSANDRA-7745
Improve PasswordAuthenticator default super user setup

patch by Aleksey Yeschenko; reviewed by Jeremiah Jordan for
CASSANDRA-7788
Validate empty cell names from counter updates

patch by Aleksey Yeschenko; reviewed by Jeremiah Jordan for
CASSANDRA-7798
Don't clear out range tombstones during compaction.

Patch by rlow; reviewed by marcuse for CASSANDRA-7808
Track expired tombstones

Patch by marcuse; reviewed by slebresne for CASSANDRA-7810
Don't allow marking already compacted sstables as compacting.

Patch by marcuse; reviewed by yukim for CASSANDRA-7145
Don't index tombstones.

patch by Mikhail Stepura; reviewed by Aleksey Yeschenko for CASSANDRA-7828
prepare 1.2.19 release
expose auto_bootstrap as a system property override