Introduce the 'always_run' task clause.

The 'always_run' task clause allows one to execute a task even in
check mode.

While here implement Runner.noop_on_check() to check if a runner
really should execute its task, with respect to check mode option
and 'always_run' clause.

Also add the optional 'jinja2' argument to check_conditional() :
it allows to give this function a jinja2 expression without exposing
the 'jinja2_compare' implementation mechanism.

test/TestPlayBook.py

@@ -474,6 +474,37 @@ class TestPlaybook(unittest.TestCase):
 
        assert utils.jsonify(expected, format=True) == utils.jsonify(actual,format=True)
 
+
+   def test_playbook_always_run(self):
+      test_callbacks = TestCallbacks()
+      playbook = ansible.playbook.PlayBook(
+          playbook=os.path.join(self.test_dir, 'playbook-always-run.yml'),
+          host_list='test/ansible_hosts',
+          stats=ans_callbacks.AggregateStats(),
+          callbacks=test_callbacks,
+          runner_callbacks=test_callbacks,
+          check=True
+      )
+      actual = playbook.run()
+
+      # if different, this will output to screen
+      print "**ACTUAL**"
+      print utils.jsonify(actual, format=True)
+      expected =  {
+          "localhost": {
+              "changed": 4,
+              "failures": 0,
+              "ok": 4,
+              "skipped": 8,
+              "unreachable": 0
+          }
+      }
+      print "**EXPECTED**"
+      print utils.jsonify(expected, format=True)
+
+      assert utils.jsonify(expected, format=True) == utils.jsonify(actual,format=True)
+
+
    def _compare_file_output(self, filename, expected_lines):
       actual_lines = []
       with open(filename) as f:

test/playbook-always-run.yml

@@ -0,0 +1,48 @@
+---
+- hosts: all
+  connection: local
+  gather_facts: False
+  vars:
+    var_true: True
+    var_false: False
+    var_empty_str: "''"
+    var_null: ~
+
+  tasks:
+  - action: command echo ping
+    always_run: yes
+
+  - action: command echo pong 1
+
+  - action: command echo pong 2
+    always_run: no
+
+  - action: command echo pong 3
+    always_run: 1 + 1
+
+  - action: command echo pong 4
+    always_run: "''"
+
+  - action: command echo pong 5
+    always_run: False
+
+  - action: command echo pong 6
+    always_run: True
+
+  - action: command echo pong 7
+    always_run: var_true
+
+  - action: command echo pong 8
+    always_run: var_false
+
+  - action: command echo pong 9
+    always_run: var_empty_str
+
+  - action: command echo pong 10
+    always_run: var_null
+
+  # this will never run...
+  - action: command echo pong 11
+    always_run: yes
+    when: no
+