Update cassandra-env.sh.erb

Disabling xss output in nodetool.
Update cassandra.init.erb


1) Added check for C* binary
2) Added check for nodetool binary
3) Added extra pre-steps for C* service stop:
   - disable thrift
   - disable gossip
   - node drain
Merge pull request #77 from vkhatri/master

Update cassandra-env.sh.erb and cassandra.init.erb