Fix install_kubeadm_cluster to check pod readiness in cert-manager namespace

Change-Id: Ic8d03d75ce177d6dc38da77963378801fba0e2ec
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/installers/install_kubeadm_cluster.sh b/installers/install_kubeadm_cluster.sh
index 1636adf..c616c36 100755
--- a/installers/install_kubeadm_cluster.sh
+++ b/installers/install_kubeadm_cluster.sh
@@ -212,6 +212,7 @@
     time_for_failure=200    # seconds broken
     OPENEBS_NAMESPACE=openebs
     METALLB_NAMESPACE=metallb-system
+    CERTMANAGER_NAMESPACE=cert-manager
     # STACK_NAME=osm          # By default, "osm"
 
     # Equivalent number of samples