Support for passing a hostname to hermit.

[jounathaen]

AFAIK, we don't have support for retrieving the hostname in hermit yet, but I can imagine that we need this sometime.
The correct approach could be to generate unique hostnames in the hypervisor (similar to Dockers approach), and then we should pass them via hermit-entry.

Not urgent, but comments are welcome (@mkroening @stlankes)

[mkroening]

I think this would fit nicely into the kernel arguments like this:

chosen {
    bootargs = "hostname=rudolf [OTHER_KERNEL_ARGS] -- [APP_ARGS]";
}