Implement creating global packages changelog file

Implements: blueprint consolidated-packages-changelog

Change-Id: Ieaea19ac4cb78b7ac6d9f8347917d3d3c84008ab
Fix missing UBUNTU_RELEASE environment variable

That patch recovers broken ubuntu image for image provisioning.
Additionally introduces few failure checks at build time.

Change-Id: I94b24d169a12f80fe7554ad8273e9ae25d7518e6
Closes-Bug: #1391217
Merge "Implement creating global packages changelog file"
Fix output of unmet dependences, add support for 'udeb' packages.

- When debian package manager selected to install older version
  of a package, but newer version requested by other package,
  then output with error is slightly different then was expected:
  Depends: package-name (= v2.0) but (v1.0) is to be installed

- Add support for 'udeb' packages for debian-installer.
  Now *.udeb packages can be placed to the folder
  /var/www/nailgun/ubuntu/x86_64/pool/debian-installer , repository
  can be updated with the sctipt 'regenerate_ubuntu_repo' with the
  same way as for *.deb packages.
  Also 'package_testing_deb' now can be used for testing gerrit
  reviews that contain any of *.deb or *.udeb packages.

Change-Id: Ib11546f7aa75e23e7f879170416c7183ff519df7
Closes-Bug: #1391569
Merge "Fix missing UBUNTU_RELEASE environment variable"
Merge "Fix output of unmet dependences, add support for 'udeb' packages."