Add a command_line attribute to the VM object with
the command line used to start the VM.
Now /start return the object in order to get
this new attribute. And the HTTP status code
is 200 instead of 204 because 204 disallow body.
Support:
* Qemu
* Dynamips
* IOU
Ref https://github.com/GNS3/gns3-gui/issues/513
raiseHTTPConflict(text="Cannot start VM with KVM enabled because hardware virtualization (VT-x/AMD-V) is already used by another software like VMware or VirtualBox")