stestr expects --concurrency to be an int
stestr expects --concurrency to be an int

Change-Id: Ia56c182287510ffbaee412b6e2a3b1eb5ad510e0
Related: https://github.com/mtreinish/stestr/issues/231

cisco-openstack/tempest,openstack/tempest,cisco-openstack/tempest,openstack/tempest,masayukig/tempest,masayukig/tempest