Fix logging in drbd _ShutdownNet method
Fix logging in drbd _ShutdownNet method

We didn't test for failure, just always logged the output.

Reviewed-by: imsnah


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