enable vnodes by default

change environment variable to reflect the new default, and update any
tests using the old VNODES_ENABLED to use the new VNODES_DISABLED
to make decisions.
Adds restore_point_in_time setting to snapshot_test.TestArchiveCommitlog, among other cleanup.
Merge pull request #39 from AlfredChenxf/master

sstableloader test with pre_compression and post_compression
Refactors dtest.py log copying to be it's own function that tests may call when needed.
@require CASSANDRA-7013 for sstableloader_compression_*
Update @requires with full URL
Switch replication_test to @no_vnodes() annotation
@no_vnodes on simple_repair_order_preserving_test - CASSANDRA-5220
Remove most excludes on 2.0 branch
Enable snapshot_test in 2.1/trunk
Drop unused DISABLE_VNODES import in replication_test
Removing more excluded tests, document counter_tests:upgrade_test bug#
Moar dtest inclusions for 2.1/trunk
Add thrift_hsha_test ticket# and update sstablesplit_test job link
cp cassandra-2.1_test-select.cfg trunk_test-select.cfg
Make #6924 test wait for schema agreement before querying with index

Also added a variant which drops the indexed columnfamily rather
than the entire keyspace
Merge pull request #40 from beobal/fix_6924_test

Make #6924 test wait for schema agreement before querying with index