Fix connection with websocket ssl

[luisfmcalado]

When connecting with server type websocket_ssl the handshake wasn't
been made correctly. This PR solves issue #309.

[tisba]

Hi @luisfmcalado! Thanks for your bug report and fix 💕

II've been able to reproduce the issue you've described in #309 and also confirmed your fix. In case someone wants to reproduce, I've been using this configuration:

<?xml version="1.0"?>
<!DOCTYPE tsung SYSTEM "/tsung/share/tsung/tsung-1.0.dtd" []>
<tsung loglevel="debug" dumptraffic="true" version="1.0">
  <clients>
    <client host="localhost" use_controller_vm="true"/>
  </clients>

  <servers>
    <server host="test.mosquitto.org" port="8081" type="websocket_ssl" weight="1" />
  </servers>

  <load>
    <arrivalphase phase="1" duration="10" unit="second">
      <users maxnumber="1" arrivalrate="10" unit="second" />
    </arrivalphase>
  </load>

  <options>
    <option name="websocket_path" value="/"/>
    <option name="websocket_subprotocols" value="mqtt"/>
  </options>

  <sessions>
    <session name="mqtt-subscribe" weight="1" type="ts_mqtt">
      <request>
        <mqtt type="connect" clean_start="true" timeout="30" keepalive="3600"></mqtt>
      </request>

      <request><mqtt type="subscribe" topic="/tsung/#" qos="1"></mqtt></request>

      <for from="1" to="100" incr="1" var="counter">
        <request>
          <mqtt type="waitForMessages" timeout="60"></mqtt>
        </request>
      </for>

      <request><mqtt type="disconnect"></mqtt></request>
    </session>
  </sessions>
</tsung>

I've tested this then using mosquitto_pub to see if we properly receive messages:

mosquitto_pub -h test.mosquitto.org -m "hello tsung" -t '/tsung/test'