Add Ignition options to create partition or RAID volume only if missing

Issue by @travisgroth

Issue Report

Bug

Container Linux Version

# cat /etc/os-release
NAME="Container Linux by CoreOS"
ID=coreos
VERSION=1409.7.0
VERSION_ID=1409.7.0
BUILD_ID=2017-07-19-0005
PRETTY_NAME="Container Linux by CoreOS 1409.7.0 (Ladybug)"
ANSI_COLOR="38;5;75"
HOME_URL="https://coreos.com/"
BUG_REPORT_URL="https://issues.coreos.com"
COREOS_BOARD="amd64-usr"

Environment

VMware ESXi / PXE Boot

Expected Behavior

When using a storage layout which does not wipe partition tables or filesystems at boot time, the system functions normally. Example CT snippet:

storage:
  disks:
    - device: /dev/sda
      wipe_table: false
      partitions:
        - label: ETCD
          number: 1
          size: 10GiB
        - label: DOCKER
          number: 2
          size: 0

  filesystems:
    - name: etcd
      mount:
        device: /dev/disk/by-partlabel/ETCD
        format: ext4
        create:
          force: false

    - name: docker
      mount:
        device: /dev/disk/by-partlabel/DOCKER
        format: ext4
        create:
          force: true

Actual Behavior

If booted with the provided snippet, the system will hang for a long period of time and eventually reboot. I have yet to catch the screen at reboot time. As soon as I change the 'force' and 'wipe_table' to 'true', the system boots as expected, but it obviously wipes things I don't want to be wiped. A single one of those two settings will trigger this behavior. I've tested with only wipe_table as false and only a single filesystem as create=false and I get the same issue. Leaving out the options has a similar effect.

As one might imagine, I'm trying to carve off persistent space for etcd to live on a master while doing a fresh format on the docker volume to keep things clean.

Reproduction Steps

1. Create CLC config specifying a device without wipe_table set to true || Create a CLC config specifying a filesystem without a 'force' set to true
2. Transpile into ignition (tested with 0.4.2, which transpiles into 2.0.0 ignition)
3. Boot system. It will hang approximately after the RNG initializes

Other Information

Start by reproducing the issue with the provided CLC storage configuration, first leaving wipe_table or filesystem create.force unset or false, then transpiling it with Ignition 0.4.2 and booting the system. Compare the behavior with both options set to true. Done means existing partition tables and filesystems are preserved while missing partitions or volumes are created and the system boots normally.