kiji-schema: SCHEMA-906. Skip the cassandra-maven-plugin and hbase-m-p correctly in cassandra submodule.

issue: https://jira.kiji.org/browse/SCHEMA-906
review: https://review.kiji.org/r/2100
commit: https://github.com/kijiproject/kiji-schema/commit/a454ecfe64e806fd5f2ed7d6de0584d490edc7da