Node will register itself, if not already done, to the SlapOS Master defined in configuration file, and will generate SlapOS configuration file.
XXX-Cedric should be like this: If desired node name is already taken, will raise an error.
XXX-Cedric: --master-url-web url will disappear in REST API. Currently, "register" uses SlapOS master web URL to register computer, so it needs the web URL (like http://www.vifib.net)
If Node is already registered (slapos.cfg and certificate already present), issues a warning, backups original configuration and creates new one.
* Register computer named "mycomputer" to another SlapOS master accessible via https://slap.myownslaposmaster.com (Note that this address should be the "slap" webservice URL, not web URL)::
* Register computer named "mycomputer" to another SlapOS master accessible via https://www.myownslaposmaster.com, and SLAP webservice accessible via https://slap.myownslaposmaster.com (Note that this address should be the "slap" webservice URL, not web URL)::