A recent review of related changes noted that we should split the creation
(or generation) of the master key into the qemuProcessPrepareDomain and leave
the writing of the master key for qemuProcessPrepareHost.

Made the adjustment and modified some comments to functions that have
changed calling parameters, but didn't change the intro doc.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>