Increase the number of threads to 25
Increase the number of threads to 25

Since our locks are not gathered nicely, we can have jobs that are
actually blocking on locks (parallel burnin shows this), so at least we
need to increase the number of threads above the usual number of jobs we
could have in a such a case.

Reviewed-by: imsnah

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