Fix firewall check

Use command module instead of shell since we do not do anything fancy
here. Remove the duplicate register.

Signed-off-by: Sébastien Han <seb@redhat.com>

roles/ceph-common/tasks/checks/check_firewall.yml

@@ -1,6 +1,6 @@
 ---
 - name: check if nmap is installed
-  shell: "command -v nmap"
+  command: "command -v nmap"
   changed_when: false
   failed_when: false
   register: nmapexist
@@ -16,7 +16,6 @@
   failed_when: false
   with_items: groups.{{ mon_group_name }}
   register: monportstate
-  register: monportstate
   when: mon_group_name in group_names
 
 - name: fail if monitor port is filtered