Replace a cfg.AddInstance with UpdateInstance
Replace a cfg.AddInstance with UpdateInstance

This seems to be the last (deprecated) use of AddInstance in order to
update an instance.

The patch also removes a whitespace-at-eol case.

Reviewed-by: ultrotter

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