qmp: make block job command naming consistent

qmp: make block job command naming consistent

The block streaming and job commands used '_' instead of '-' for reasons
of compatibility with libvirt, which already included support for the
'_' naming.  However, the semantics of block_job_cancel have changed and
libvirt now needs to handle the new semantics.

Since the old semantics were never in a QEMU release we can still rename
the commands to use '-' instead of '_'.  Libvirt is also happy because
the new name can be used to distinguish QEMU binaries that support the
latest block-job-cancel semantics from those that include a downstream
block_job_cancel command.

Therefore, let's apply the QAPI/QMP naming rules to the block streaming
and job commands.  QEMU 1.1 will be the first release with these
commands so no upstream users can break.

Note that HMP commands are left with '_' because that is the convention
there.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>