Add Exec task
Add Exec task

In order to remote execute arbitrary commands a new task needed to be added
to the list of tasks.

I have tested this using a suite that contained the following task definition:

```
    test_exec:
      class: F500\CI\Task\Exec\ExecTask
      name: Run exec test
      cwd: %remote_root_dir%
      bin: ls
      args: ['-lha']
      parsers:
        always_pass:
          class: F500\CI\Task\AlwaysPassResultParser
      wrappers: [ansible]
```

And I verified the output by checking var/logs/app.dev.log

f500/future-ci,f500/future-ci,f500/future-ci