User limits to be setup conditionally and few other things

[pielu]

Make Cassandra's user limits to be setup conditionally in case user already manages users in different cookbook / way (avoid limits duplication)

Also, the libraries to be (sym)linked as Cassandra's user and to have world readable permissions (otherwise Cassandra fails to load them)

Last but not least, fill gaps in tarballs checksums and some more linter-happy formatting.

[michaelklishin]

Thank you!