curtin 18.1

- zfs/zpool version=28 by default, allow users to override default values.
  (LP: #1754013)
- helpers/shell-archive: drop use of tar --sparse flag (LP: #1757565)
- vmtest: In Basic install, add entry for swap to fstab and verify its use.
- vmtest: skip some bcache tests pending kernel fixes
- vmtests: extend skip_by_date for lvmroot_xfsroot and network_mtu
- vmtest: fix pollinate re.search to use groupdict()
- Add pollinate user-agent configuration support.
- vmtest: Remove xenial and trusty specific workaround for rooturl.
- vmtest: Add Filesystem Battery test.
- Remove grub2/xenial specific workarounds for zfsroot.
- Disable dirty_disks mode for mdadm + iscsi tests
- tools/curtainer: Try harder to get source at binary version.
- clear_holders: wipe complex devices before disassembly (LP: #1750519)
- vmtests: network_mtu: fix bug number and move date out one month
- fix /usr/bin/curtin exit code in install failure (LP: #1751176)
- docs: Document use of format command with fstype: zfsroot
- docs: Add HACKING.rst doc to top level dir and readthedocs.
- vmtest: fix centos root-tgz image sync
- block_meta: Ensure offset input to sgdisk are integers.
- Fix error in url_helper and vmtest from previous commit.
- tools: fix curtainer to specify source version to apt-get source.
- Add support for installing sources that are a filesystem image.
  (LP: #1746348)
- clear-holders: detect and remove devices from kernel swap as needed.
  (LP: #1743643)
- tests: remove xfs filesystem from basic uefi test.
- tools: fix curtainer --source with trusty.
- apply_net: do not write to stderr directly.
- vmtest: Drop use of root-image.gz and maas2roottar.
- in-target: use ChrootableTarget so that unshare pid is used.
- tools/curtainer: check that binary and source version are the same.
  (LP: #1747077)
- Add zfsroot as a filesystem type
- fix modeline for shell syntax files.
- error logs: Create error_tarfile path if path does not exist
  (LP: #1746363)
- zfs: only load zfs on xenial+ skip artful/bionic zfs env export
- error logs: automatically collect and tar curtin logs upon error.
- vmtests: Support skipping skip_by_date tests based on environment.
- Add zpool, zfs storage commands for experimental support of ZFS on root.
- tests: revert workaround for bug in overlayroot that is now fixed.
- tests: Bump skip_by_dates for bug 1652822 and 1671952.
- cli: add curtin collect-logs sub-command
- vmtest: Do not run tests of unsupported Ubuntu releases.
- Make license headers and file footers consistent and simplify.
- tests: cleanup the apt custom sources test.
- apt: Be more lenient when replacing mirrors in /etc/apt/sources.list
  (LP: #1744038)
- vmtest: Drop Zesty release
- vmtest: initialize logger with class names for easy parsing
- packaging: Do not mention primary contributors in debian/changelog.
- packaging: Update new-upstream-snapshot to work with git.
- Bump pylint to 1.8.1.
- vmtests: switch to MAAS v3 streams for images and kernels
- tests: update pack tests to clear out pyc files more completely.
- debian/control: drop conflicts that had bzr version
- Switch uses of bzr to git, borrow from cloud-init git workflow.