SSH: Don't allow connectToHost() while already connecting/connected.

Also fix callers potentially violating this policy.

Change-Id: I630f1c544885df93a81e217e792363c0c2314108
Reviewed-on: http://codereview.qt.nokia.com/1186
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Daniel Teske <daniel.teske@nokia.com>

src/libs/utils/ssh/sshconnection.cpp

@@ -620,6 +620,8 @@ void SshConnectionPrivate::sendKeepAlivePacket()
 
 void SshConnectionPrivate::connectToHost()
 {
+    QTC_ASSERT(m_state == SocketUnconnected, return);
+
     m_incomingData.clear();
     m_incomingPacket.reset();
     m_sendFacility.reset();