When the daemon libvirtd restarts, a connected virsh gets a SIGPIPE
and dies. This change the behaviour to try to reconnect if the
signal was received or command error indicated a connection or RPC
failure. Note that the failing command is not restarted.

* tools/virsh.c: catch SIGPIPE signals as well as connection related
  failures, add some automatic reconnection code and appropriate error
  messages.