telnet and netcat support for secondary connections
As well as SSH, support telnet and netcat connections from the dispatcher to the guest to lower the barrier for test image support.
For telnet, the dispatcher needs to specify the destination (using the multinode API to get the IP) of that specific job - the port can come from the test writer. Must prevent random telnet connections to other hosts.
Investigate similar support for netcat, boundaries, limitations and security implications.
Migrated from https://projects.linaro.org/browse/LAVA-516