The current output of 'blockjob [--info]' is a single line
designed for human consumption; it's not very nice for machine
parsing.  Furthermore, I have plans to modify the line in
response to the new flag for controlling bandwidth units.
Solve that by adding a --raw parameter, which outputs
information closer to the C struct.

$ virsh blockjob testvm1 vda --raw
 type=Block Copy
 bandwidth=1
 cur=197120
 end=197120

The information is indented, because I'd like for a later patch
to add a mode that iterates over all the vm's disks with status
for each; in that mode, each block name would be listed unindented
before information (if any) about that block.

Now that we have a raw mode, we can guarantee that it won't change
format over time.  Any app that cares about parsing the output can
try --raw, and if it fails, know that it was talking to an older
virsh and fall back to parsing the human-readable format which had
not changed until now; meanwhile, when not using --raw, we have
freed future virsh to change the output to whatever makes sense.

My first change to human mode: this command now guarantees a line
is printed on successful use of the API, even when the API did
not find a current block job (consistent with the rest of virsh).

Bonus: https://bugzilla.redhat.com/show_bug.cgi?id=1135441
complained that this message was confusing:

$ virsh blockjob test1 hda  --async --bandwidth 10
error: conflict between --abort, --info, and --bandwidth modes

even though the man page already documents that --async implies
abort mode, all because '--abort' wasn't present in the command
line.  Since I'm adding another case where options are tied
to or imply a mode, I changed that error to:

error: conflict between abort, info, and bandwidth modes

* tools/virsh-domain.c (cmdBlockJob): Add --raw parameter; tweak
error wording.
* tools/virsh.pod (blockjob): Document it.
Signed-off-by: NEric Blake <eblake@redhat.com>