Scope exim service name variable

This is used in a handler which may be run after intervening roles;
ensure it has a unique variable name.

Change-Id: I6a3d856d3252ff62220d9769232e31ea7c4f9080

roles/exim/handlers/main.yaml

@@ -1,4 +1,4 @@
 - name: Restart exim
   service:
-    name: "{{ service_name }}"
+    name: "{{ exim_service_name }}"
     state: restarted

roles/exim/tasks/main.yaml

@@ -36,5 +36,5 @@
 
 - name: Enable exim
   service:
-    name: "{{ service_name }}"
+    name: "{{ exim_service_name }}"
     enabled: true

roles/exim/vars/Debian.yaml

@@ -1,5 +1,5 @@
 package: exim4-daemon-light
-service_name: exim4
+exim_service_name: exim4
 config_file: /etc/exim4/exim4.conf
 conf_dir: /etc/exim4
 sysdefault_file: /etc/default/exim4

roles/exim/vars/RedHat.yaml

@@ -1,5 +1,5 @@
 package: exim
-service_name: exim
+exim_service_name: exim
 config_file: /etc/exim/exim.conf
 conf_dir: /etc/exim/
 sysdefault_file: /etc/sysconfig/exim