Test parallel instance creation with --opportunistic-locking
Test parallel instance creation with --opportunistic-locking

With the recent changes, opportunistic locking should not
require retries any more on clusters that have enough capacity.
So it is fair to add the --opportunistic-locking option the
parallel instance creation tests. In this way, we
- verify that the absence of the need to retry is indeed true and
- get a realistic performance measurement for truly parallel
  instance creation.

Signed-off-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>
Reviewed-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>

Cherry-picked from 37d6f7f5f7ebfc3f40b70c28930a99045aa1cd01.

Signed-off-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>
Reviewed-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>

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