virsh: Split cmds of domain group from virsh.c

virsh: Split cmds of domain group from virsh.c

This splits commands to manage domain into virsh-domain.c,The helpers
not for common use are moved into them too. Standard copyright is added
for the new file.

* tools/virsh.c:
  - Remove commands for domain group, and one helper
    (vshDomainVcpuStateToString)
  - vshStreamSink is moved before commands's definition for it's
    also used by commands not of domain group, such as volUpload.

* tools/virsh-domain.c:
  - New file, commands for domain group and the one helper are
    moved into it.

* po/POTFILES.in:
  - Add virsh-domain.c

* cfg.mk:
  - Skip to check config.h including for virsh-domain.c