log: include hostname in initial log message
    
    On the very first log message we send to any output, we include
    the libvirt version number and package string. In some bug reports
    we have been given libvirtd.log files that came from a different
    host than the corresponding /var/log/libvirt/qemu log files. So
    extend the initial log message to include the hostname too.
    
    eg on first log message we would now see:
    
     $ libvirtd
     2015-12-04 17:35:36.610+0000: 20917: info : libvirt version: 1.3.0
     2015-12-04 17:35:36.610+0000: 20917: info : hostname: dhcp-1-180.lcy.redhat.com
     2015-12-04 17:35:36.610+0000: 20917: error : qemuMonitorIO:687 : internal error: End of file from monitor
    
    Signed-off-by: Daniel P. Berrange <berrange@redhat.com>