connectionmanager: call callbacks when account is disabled

If an account is disabled during the initialization of the ICE,
the callacks must be called to correctly clean conversation_module.
This was not correctly done as we only check the onShutdown() after
that the TLSSocketEndpoint is initialized.
It was a problem when the account was disabled, because in
connectDeviceStartIce() isDestroying_ was true at this point, so
we didn't erase the pending callback.

Change-Id: I21cdd30057d9879b6d6fef189fc43bf916d4c310