cc_mounts should ensure_dir on lower, upper and workdir params

This bug was originally filed in Launchpad as [LP: #1695277](https://bugs.launchpad.net/cloud-init/+bug/1695277)

Launchpad details

affected_projects = []

assignee = None

assignee_name = None

date_closed = None

date_created = 2017-06-02T14:03:10.564908+00:00

date_fix_committed = None

date_fix_released = None

id = 1695277

importance = low

is_complete = False

lp_url = https://bugs.launchpad.net/cloud-init/+bug/1695277

milestone = None

owner = raharper

owner_name = Ryan Harper

private = False

status = confirmed

submitter = raharper

submitter_name = Ryan Harper

tags = []

duplicates = []

_Launchpad user **Ryan Harper(raharper)** wrote on 2017-06-02T14:03:10.564908+00:00_

Ubuntu Trusty 14.04 machine that mounts an overlayfs at /var/spool/postfix, and this works great:

fs_setup:
- label: postfix
device: /dev/xvde
filesystem: ext4
mounts:
- [ /dev/xvde, /mnt/postfix-overlay ]
- [ overlayfs, /var/spool/postfix, "overlayfs", "defaults,lowerdir=/var/spool/postfix,upperdir=/mnt/postfix-overlay", "0", "2" ]
mount_default_fields: [ None, None, "auto", "defaults,nobootwait", "0", "2” ]

Upgrading the system image to Xenial 16.04 causes the overlayfs to fail to mount with the error “missing ‘workdir’”.

Turns out, between Trusty and Xenial, the “workdir” directory in overlayfs went from optional to mandatory, and now the system no longer deploys.

What needs to happen is that after the fs_setup step that creates /mnt/postfix-overlay, but before the mounts section where the overlayfs is created, the workdir and upperdir directories need to be created on the /mnt/postfix-overlay disk as /mnt/postfix-overlay/upperdir and /mnt/postfix-overlay/workdir (or something) respectively.