CDH-19348 LDAP + SSL

TSSLSocket should not be "opened" if it's used by the server. See TSSLSocket::open()

Therefore, in TSaslTransport::open(), it should not open underlying transport if it's a sever.

I've tested it manually with LDAP and LDAP+SSL, but we don't have functional test for LDAP yet.

Change-Id: Ifee4957c6a874df47760d33ab50aa90eb7eda617
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2718
Reviewed-by: Alan Choi <alan@cloudera.com>
Tested-by: jenkins