Handle Ubuntu 14.04 w/ linux-aws kernel package

When using the linux-aws kernel package for EC2 instances, there are no
linux-image-extra packages. However, the kernel image package itself already
contains AuFS support, so the installation can just be skipped.

tasks/main.yml

@@ -41,7 +41,8 @@
  with_items:
  - linux-image-extra-{{ ansible_kernel }}
  - linux-image-extra-virtual
- when: docker_aufs_enabled and ansible_distribution_version is version_compare('14.04', '==')
+ when: docker_aufs_enabled and ansible_distribution_version is version_compare('14.04', '==') and ansible_kernel is version_compare('4.4', '<')
+
  register: linux_image_extra_install
  ignore_errors: yes