Feature Request: Read configuration from file

[xiaoke]

command line:

$ vmcli --config ubuntu/vm.conf

shutdown-timeout=15
cpu-count=1
memory-size=256
kernel=kernel
initrd=rootfs
disk=disk-0.img
disk=disk-1.img
network=e6:64:3d:68:5c:78@nat
cmdline=console=hvc0 irqfixup root=/dev/vda