package installation path of python scripts

[syuu1228]

Currently we installs filter_cassandra_attributes.py and cassandra_attributes.py under /usr/bin, and soon we add cqlsh.py to there.
But I think user doesn't call them directly from shell, it's indirectly invoked by other scripts.
Maybe it's better to move somewhere else, like /usr/share/scylla/cassandra/ which currently used for placing *.jar files and cassandra.in.sh.