x509 certificate support for iot device simulation and send-d2c-message

Added x509 thumbprint and x509 ca device support for iot device simulation and send-d2c-message.

Other things added/changed:

moved everything iot device from hub.py to iothub folder
added optional parameter for the device symmetric key for simulating devices. This will skip looking up the device for the symmetric key. (note that there is still a look up for the iot hub hostname)
split unit tests (and fix them based on the new paths)
fix int tests based on new inputs
create a method to quickly parse out the monitor output into the json monitor events
update execute_on_thread to take in a dictionary of args - removing the need to put 4-5 None's

Next steps: implement name or hostname for iot hub, remove hostname lookup if the hub hostname is provided already.

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Azure / azure-iot-cli-extension