Some improvements on Console / HDD disk device

[brenard]

I made some improvements during my recent integrations of WebVirtMgr and I forget to make a pull request. So, this pull request address different topics :

• I unified VNC and Spice console interfaces with bootstrap. In the same goal, I add some Crtl+Alt+FX send keys features in VNC console (already exists in Spice console)
• I fix console access on instance running on hypervisor access thought local UNIX socket
• I add possibility to define HDD cache mode during instance creation
• I improve RBD disk device definition on instance creation :
  • All RBD monitor hosts is retrieve from RBD pool definition, not only the first
  • RBD port of monitor hosts is not hard coded but retrieve from pool definition