xenapi: set viridian=false for linux servers

Currently all servers get:
viridian=true

This is the hyper-v awareness inside windows Xen uses to get better
windows peformance. However this can make linux guests think they are
running on hyper-v.

So, this change ensures all linux guests get viridian=false

implements blueprint xenapi-support-linux-hvm
Change-Id: I4e2b0b9b03d14a3d8679667395bdb7a831af48ca
Merge "xenapi: set viridian=false for linux servers"