Please backport btrfs-tools 4.3-1 (main) from xenial

[bhueske]

Please backport btrfs-tools 4.3-1 (main) from xenial to trusty.

Reason for the backport:
========================
With the linux-generic-lts-wily HWE, there is a 4.2 Kernel availaby for trusty. BTRFS has many improvements at the 4er kernel branch. The btrfs-tools (3.12) available in Trusty are too old and the full functionality of btrfs can not be used.

Testing:
========
Mark off items in the checklist [X] as you test them, but please leave the checklist so that backporters can quickly evaluate the state of testing.

You can test-build the backport in your PPA with backportpackage:
$ backportpackage -u ppa:<lp username>/<ppa name> -s xenial -d wily btrfs-tools

* wily:
[ ] Package builds without modification
[ ] btrfs-tools installs cleanly and runs
[ ] btrfs-tools-udeb installs cleanly and runs
[ ] btrfs-tools-dbgsym installs cleanly and runs
[ ] btrfs-tools-udeb-dbgsym installs cleanly and runs
[ ] btrfs-tools-dbg installs cleanly and runs

Reverse dependencies:
=====================
The following reverse-dependencies need to be tested against the new version of btrfs-tools. For reverse-build-dependencies (-Indep), please test that the package still builds against the new btrfs-tools. For reverse-dependencies, please test that the version of the package currently in the release still works with the new btrfs-tools installed. Reverse- Recommends, Suggests, and Enhances don't need to be tested, and are listed for completeness-sake.

btrfs-tools
-----------
* udisks2
  [ ] wily (Reverse-Suggests)
* btrbk
  [ ] wily (Reverse-Depends)
* libsnapper2v5
  [ ] wily (Reverse-Depends)
* xen-tools
  [ ] wily (Reverse-Suggests)
* libguestfs0
  [ ] wily (Reverse-Depends)
* apt-btrfs-snapshot
  [ ] wily (Reverse-Depends)
* libguestfs
  [ ] wily (Reverse-Build-Depends)
* mythbuntu-live
  [ ] wily (Reverse-Depends)
* snapper
  [ ] wily (Reverse-Build-Depends)
* ubiquity
  [ ] wily (Reverse-Recommends)
* fsarchiver
  [ ] wily (Reverse-Suggests)
* lxc
  [ ] wily (Reverse-Suggests)
* schroot
  [ ] wily (Reverse-Suggests)
* kvpm
  [ ] wily (Reverse-Suggests)
* system-storage-manager
  [ ] wily (Reverse-Depends)
* docker.io
  [ ] wily (Reverse-Suggests)
  [ ] wily (Reverse-Build-Depends)
* linaro-image-tools
  [ ] wily (Reverse-Recommends)

btrfs-tools-udeb
----------------

btrfs-tools-dbgsym
------------------

btrfs-tools-udeb-dbgsym
-----------------------

btrfs-tools-dbg
---------------