Modify replication_admin.rb to use ReplicationPeerConfigBuilder

Error: test_append_peer_namespaces:_works_with_namespaces_array(Hbase::ReplicationAdminTest): Java::JavaLang::UnsupportedOperationException:
java.util.Collections$UnmodifiableCollection.add(java/util/Collections.java:1055)
java.lang.reflect.Method.invoke(java/lang/reflect/Method.java:498)
org.jruby.javasupport.JavaMethod.invokeDirectWithExceptionHandling(org/jruby/javasupport/JavaMethod.java:453)
org.jruby.javasupport.JavaMethod.invokeDirect(org/jruby/javasupport/JavaMethod.java:314)
RUBY.block in add_peer_namespaces(/home/jenkins/jenkins-slave/workspace/HBase-Flaky-Tests/hbase-shell/src/main/ruby/hbase/replication_admin.rb:226)
org.jruby.RubyArray.each(org/jruby/RubyArray.java:1734)
org.jruby.RubyArray$INVOKER$i$0$0$each.call(org/jruby/RubyArray$INVOKER$i$0$0$each.gen)
RUBY.add_peer_namespaces(/home/jenkins/jenkins-slave/workspace/HBase-Flaky-Tests/hbase-shell/src/main/ruby/hbase/replication_admin.rb:225)
RUBY.command(/home/jenkins/jenkins-slave/workspace/HBase-Flaky-Tests/hbase-shell/src/main/ruby/shell/commands/append_peer_namespaces.rb:40)
org.jruby.RubyClass.finvoke(org/jruby/RubyClass.java:522)