blockcopy: split out virsh implementation

blockcopy: split out virsh implementation

I'm about to extend the capabilities of blockcopy.  Hiding a few
common lines of implementation gets in the way of the new required
logic, and putting the new logic in the common implementation won't
benefit any of the other blockjob operations.  Therefore, it is
simpler to just do the work inline.  There should be no semantic
change in this patch.

* tools/virsh-domain.c (blockJobImpl): Move block copy guts...
(cmdBlockCopy): ...into their lone caller.

Signed-off-by: Eric Blake <eblake@redhat.com>