supporting new windows launch scripts for #7001

Does not properly check version in common.make_cassandra_env yet. Now
that pid.txt exists, there is no need to create dirty_pid.tmp. There is
some sort of timing issue where pid.txt isn't updated until after we
read it.
Ensure pid file created and populated on windows
Ensure cassandra_conf is properly set in env ps1

cassandra-env.ps1 sets $env:CASSANDRA_CONF which we want to override to
point to .ccm/cluster/node/conf
Moved Cluster get version to helper

This change in functionality allows common.py to get the version of
cassandra without knowing the current running cluster or node.
Added logic to set correct jmx ports
Updating list of requirements with 'six'
Merge pull request #118 from lexigen/patch-1

Updating list of requirements with 'six'
Merge branch 'master' of https://github.com/ptnapoleon/ccm
Add ant to requirements

Fixes #83, #35.
Moved jmx function to prevent ps1 rewrite
Switched to full pathing for logback.xml
Ensuring backwards compatibility on windows

Changes for new launch scripts in 2.1 will not affect behavior for
versions prior to 2.1
Merge pull request #121 from ptnapoleon/master

Support new windows launch scripts from #7001
Merge pull request #120 from danielcompton/patch-1

Add ant to requirements