tools/qvm-run: factor out actual process running into separate function
tools/qvm-run: factor out actual process running into separate function

Pylint complains that main() is too long and that's indeed true. Factor
out single process call (together with all the prepartion) into separate
function and keep only common code in main().

marmarek/qubes-core-mgmt-client,marmarek/qubes-core-mgmt-client,marmarek/qubes-core-mgmt-client