KVMHypervisor: use the StopInstance retry feature
KVMHypervisor: use the StopInstance retry feature

Since we know StopInstance is going to be called more than once (at
least twice, once with force and once without, but normally quite a lot
more) we don't need our own sleep/loop, and we can just send one monitor
command per call.

Signed-off-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>
Reviewed-by: Olivier Tharan <0947fcc917eb1d3c89ad818beb61e3b2c3cf3bba@google.com>

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