[libvirt] [PATCH 0/3 v4] add 'sharePolicy' attribute for qemu vnc sharing policy

[Guannan Ren]

v3->v4
  add missing .args, .xml files
  (I raw it in git Untracked files this morning and
   thought about it for a while, then git-cleaned them...)
  rebase work.

v2->v3
  rebase work.

v1->v2:
  changed attribute name from 'policy' to 'sharePolicy'
  renamed caps flag name: QEMU_CAPS_VNC_SHARE_POLICY
  fixed issues pointed out in v1 review
  have to keep hard-coded version probe after checking qemu -help and qmp command.

As there were some vnc patches recently, I chose do rebase work a little later.

These patches try to add a new attribute 'sharePolicy' to element graphics of
vnc type. This attribute has three values:
allow-exclusive,force-shared and ignore.