Add a new feature to mirror-copy and mirror-write. If the target PFS does

Add a new feature to mirror-copy and mirror-write.  If the target PFS does
not exist these directives will now ask you whether you want to create it
or not, providing a VERY convenient method for creating a new slave PFS.

WARNING! This adds another packet to the protocol to make the initial
handshake symmetrical, allowing the target to get information on the
originator's shared-uuid before the operation is initiated.  If running
to or from a remote host both sides must be running the same version of
the hammer utility.

Submitted-by: Michael Neumann <mneumann@ntecs.de>