Correct issue of handlers running on all hosts incorrectly

Also adds an integration test to catch this bug in the future.

Fixes #7559

test/integration/roles/test_handlers/meta/main.yml

@@ -1,3 +1,2 @@
-dependencies: 
-  - prepare_tests
+dependencies: []
 

test/integration/roles/test_handlers/tasks/main.yml

@@ -16,8 +16,23 @@
 # You should have received a copy of the GNU General Public License
 # along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
 
-- name: notify the handler
+
+- name: reset handler_called variable to false for all hosts
+  set_fact:
+    handler_called: False
+
+- name: notify the handler for host A only
   shell: echo
   notify: 
     - set handler fact
+  when: inventory_hostname == 'A'
 
+- name: force handler execution now
+  meta: "flush_handlers"
+
+- debug: var=handler_called
+
+- name: validate the handler only ran on one host
+  assert:
+    that:
+    - "inventory_hostname == 'A' and handler_called == True or handler_called == False"