ansible: use _ansible_shell_executable in ScriptRunner.

Now we match Ansible error output and exit status. Ansible:

    $ ansible localhost -e end=2 -m custom_binary_single_null
    localhost | FAILED! => {
        "changed": false,
        "module_stderr": "Shared connection to localhost closed.\r\n",
        "module_stdout": "/bin/sh: /Users/dmw/.ansible/tmp/ansible-tmp-1522661797.42-158833651208060/custom_binary_single_null: cannot execute binary file\r\n",
        "msg": "MODULE FAILURE",
        "rc": 126
    }

Mitogen now:

    localhost | FAILED! => {
        "changed": false,
        "module_stderr": "/bin/sh: /var/folders/gw/f6w3dgy16fsg5y4kdthbqycw0000gn/T/ansible_mitogenAYF8LM-binary: cannot execute binary file\n",
        "module_stdout": "",
        "msg": "MODULE FAILURE",
        "rc": 126
    }

Previously:

    localhost | FAILED! => {
        "changed": false,
        "module_stderr": "<type 'exceptions.OSError'>: [Errno 8] Exec format error",
        "module_stdout": "",
        "msg": "MODULE FAILURE",
        "rc": 1
    }

ansible_mitogen/runner.py

@@ -214,7 +214,11 @@ class ProgramRunner(Runner):
         )
 
     def _get_program_args(self):
-        return [self.program_fp.name]
+        return [
+            self.args['_ansible_shell_executable'],
+            '-c',
+            self.program_fp.name
+        ]
 
     def revert(self):
         """
@@ -229,6 +233,7 @@ class ProgramRunner(Runner):
                 args=self._get_program_args(),
             )
         except Exception, e:
+            LOG.exception('While running %s', self._get_program_args())
             return {
                 'rc': 1,
                 'stdout': '',
@@ -267,7 +272,11 @@ class ArgsFileRunner(Runner):
         return json.dumps(self.args)
 
     def _get_program_args(self):
-        return [self.program_fp.name, self.args_fp.name]
+        return [
+            self.args['_ansible_shell_executable'],
+            '-c',
+            "%s %s" % (self.program_fp.name, self.args_fp.name),
+        ]
 
     def revert(self):
         """