[branch-1] make hbase-thrift optional in hbase-assembly module

[ERROR] Failed to execute goal on project hbase-assembly: Could not resolve dependencies for project org.apache.hbase:hbase-assembly:pom:1.7.0: Failure to find org.apache.hbase:hbase-thrift:jar:1.7.0 in https://repository.apache.org/content/repositories/releases/ was cached in the local repository, resolution will not be reattempted until the update interval of apache release has elapsed or updates are forced -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/DependencyResolutionException