Allow user to call lcb_connect() several times safely

Change-Id: I2937ddbcb38d7ab716807a8d8a65bfb5a5a3cc10
Reviewed-on: http://review.couchbase.org/28303
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>