ShutdownInstance: report hypervisor error
ShutdownInstance: report hypervisor error

When StopInstance raises an HypervisorError, report it in the logged
message to ease with debugging.

Reviewed-by: iustinp


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