virsh: Notify users about disconnects
    
    After my "client rpc: Report proper error for keepalive disconnections"
    patch, virsh would no long print a warning when it closes a connection
    to a daemon after a keepalive timeout. Although the warning
    
        virsh # 2015-09-15 10:59:26.729+0000: 642080: info :
        libvirt version: 1.2.19
        2015-09-15 10:59:26.729+0000: 642080: warning :
        virKeepAliveTimerInternal:143 : No response from client
        0x7efdc0a46730 after 1 keepalive messages in 2 seconds
    
    was pretty ugly, it was still useful. This patch brings the useful part
    back while making it much nicer:
    
    virsh # error: Disconnected from qemu:///system due to keepalive timeout
    
    Signed-off-by: Jiri Denemark <jdenemar@redhat.com>