Fix allow_retrieve_keytab_host in service module.

The attribute `allow_retrieve_keytab_host` was not working due to
wrong processing of the input and verification if the values should
be updated. Both the issues are fixed by this change.

Tests were added to better verify service keytab members.

tests/service/env_vars.yml

@@ -0,0 +1,15 @@
+---
+    - name: Get Domain from server name
+      set_fact:
+        test_domain: "{{ ansible_fqdn.split('.')[1:] | join('.') }}"
+
+    - name: Set host1, host2 and svc hosts fqdn
+      set_fact:
+        host1_fqdn: "{{ 'host1.' + test_domain }}"
+        host2_fqdn: "{{ 'host2.' + test_domain }}"
+        svc_fqdn: "{{ 'svc.' + test_domain }}"
+        nohost_fqdn: "{{ 'nohost.' + test_domain }}"
+
+    - name: Get IPv4 address prefix from server node
+      set_fact:
+        ipv4_prefix: "{{ ansible_default_ipv4.address.split('.')[:-1] | join('.') }}"