fixes switch.is_connected method to check if connection exists first.
fixes switch.is_connected method to check if connection exists first.

cemsbr/kytos,renanrodrigo/kytos,erickvermot/kytos,cemsbr/kytos,diraol/kytos,erickvermot/kytos,diraol/kytos,kytos/kytos,cemsbr/kytos,macartur/kytos,erickvermot/kytos,diraol/kytos,kytos/kyco