Add cluster parameter change workload
Add cluster parameter change workload

One of the few leftover unused RAPI methods is the cluster modify
method. This patch tests it by setting and unsetting various safe
values.

Signed-off-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>
Reviewed-by: Helga Velroyen <2d0126b1ec6f9ec5cbec4a7012aa14faeaef10f5@google.com>

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