blockjob: split up virsh blockjob info
    
    I have plans to make future enhancements to the job list mode,
    which will be easier to do if the common blockJobImpl function
    is not mixing a query command with multiple modify commands.
    Besides, it just feels weird that all callers to blockJobImpl
    had to supply both a bandwidth input argument (unused for info
    mode) and an info output argument (unused for all other modes);
    not to mention I just made similar cleanups on the libvirtd
    side.
    
    The only reason blockJobImpl returned int was because of info
    mode returning -1/0/1 (all other job API are -1/0), so that
    can also be cleaned up.  No user-visible changes in this commit.
    
    * tools/virsh-domain.c (blockJobImpl): Change signature and return
    value.  Drop info handling.
    (cmdBlockJob): Handle info here.
    (cmdBlockCommit, cmdBlockCopy, cmdBlockPull): Adjust callers.
    
    Signed-off-by: Eric Blake <eblake@redhat.com>