Add support for formating/parsing libxl channels.

Syntax on xen libxl goes as following:
channel=["connection=pty|socket,path=/path/to/socket,name=XXX",...]
Signed-off-by: NJoao Martins <joao.m.martins@oracle.com>
Acked-by: NJim Fehlig <jfehlig@suse.com>
Signed-off-by: NJim Fehlig <jfehlig@suse.com>