Fix class methods in KVM hypervisor
Fix class methods in KVM hypervisor

Several methods in KVM hypervisor behave like 'classmethods', however,
they did not have the '@classmethod' annotation.  This patch adds
'@classmethod' annotations to several of these methods with the goal
of making '_StopInstance' available to the QA.  This step is necessary
for the QA test for instance shutdown detection on KVM.

Signed-off-by: Jose A. Lopes <0fb9c4f8511df4ec2ae28af879e9d462f6218a2c@google.com>
Reviewed-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>

apyrgio/ganeti,bitemyapp/ganeti,ganeti/ganeti,yiannist/ganeti,andir/ganeti,yiannist/ganeti,mbakke/ganeti,andir/ganeti,apyrgio/ganeti,grnet/snf-ganeti,onponomarev/ganeti,ganeti-github-testing/ganeti-test-1,ganeti/ganeti,leshchevds/ganeti,ganeti-github-testing/ganeti-test-1,mbakke/ganeti,grnet/snf-ganeti,yiannist/ganeti,dimara/ganeti,andir/ganeti,mbakke/ganeti,dimara/ganeti,leshchevds/ganeti,bitemyapp/ganeti,leshchevds/ganeti,ganeti/ganeti,onponomarev/ganeti