Slightly improved message when parsing properties for DDL queries

patch by boneill42; reviewed by slebresne for CASSANDRA-6453
caching all calls of cloneOnlyTokenMap is not correct since many callers mutate the result
patch by Aleksey Yeschenko; reviewed by jbellis for CASSANDRA-6488
merge from 1.2
Simplify TokenMetadata.cachedOnlyTokenMap()
Merge branch 'cassandra-1.2' into cassandra-2.0