Do not append "-{release}" if cassandra.release is empty/nil.
Do not append "-{release}" if cassandra.release is empty/nil.

* Datastax has stopped appending "-{release}" tags
  in their version numbering.
* This change only appends "-{release}" if
  cassandra.release is not empty/nil.

adityagodbole/cassandra-chef-cookbook,adityagodbole/cassandra-chef-cookbook,michaelklishin/cassandra-chef-cookbook,criteo-forks/cassandra-chef-cookbook,vdemonchy/cassandra-chef-cookbook,vkhatri/cassandra-chef-cookbook,vdemonchy/cassandra-chef-cookbook,michaelklishin/cassandra-chef-cookbook,michaelklishin/cassandra-chef-cookbook,jfwm2/cassandra-chef-cookbook,jfwm2/cassandra-chef-cookbook,criteo-forks/cassandra-chef-cookbook,adityagodbole/cassandra-chef-cookbook,criteo-forks/cassandra-chef-cookbook,jfwm2/cassandra-chef-cookbook,vdemonchy/cassandra-chef-cookbook,vkhatri/cassandra-chef-cookbook,vkhatri/cassandra-chef-cookbook