The purpose of the added script is to shorten calling neoctl by removing the
need to constantly supply things SlapOS can provide on its own like
certificates and admin address. A sample command is now as simple as:

    ~/srv/runner/instance/slappartX/bin/neoctl set cluster STARTING_BACKUP

/reviewed-on !120

As `setuptools.archive_util.unpack_archive` (or self.extract
from slapos.recipe.build) is not able to handle .tar.xz archives,
tar component is added to wkhtmltopdf build dependencies.

As wkhtmltopdf sometimes needs to get files in
current working directory ONLY, this has to be
set correctly.

E.g. `wkhtmltopdf toc --xsl-style-sheet no_absolute_path.xsl input.html output.pdf`

After some upstream refactoring, a #include is missing (at least up to 2.3.14),
but still pulled implicitely when openssl is built with engines. This commit
fixes the configure step, so that HAVE_OPENSSL_ENGINE is true as expected.

More on https://community.openvpn.net/openvpn/ticket/792

/reviewed-on nexedi/slapos!122

This reverts commit 7f6729de.

ZODB has been switched to ZODB4 in 447b27e6 (Switch from ZODB3 (3.10.7)
to ZODB (4.4.4)) including raising transaction version requirement to
1.7.0 so we can try to introduce zodbtools one more time.

/proposed-for-review-on nexedi/slapos!121

Without it, the interest of tweaking the partition table is limited, because:
- it is impossible to free space efficiently
- 'optimize table' is even slower

slaprunner: export script shouldn't succeed if the backup of the contained instances are running at the same time

- version up: setuptools 30.1.0
- revert commit 1d0a8073

NEO is also not ready yet for transaction 2.x

This MR brings some confort of use and of administration for the resiliency stack and resiliency related taks :

   *  logrotate some logs/feeds to save disk space
   * adds more promises on export and import instances
   * improves feedback on import failures :  promises are more verbose, more information on the takeover webpage, ...
   * better indempotency for the backup time information, which is now published instead of read from the .installed.cfg

Updated on 11/22 : 

   * improve pbs recipe : makes the trap command cross-shell
   * remove infinite loops in scripts generated by pbs, but run a given amount of time until raising an error (which can be catched by promises)
   * runner-importer script doesn't systematically fails if there is no requested SR.
   * adds promises for notifier feeds (on exporter and pbs) to check last result and check if feed is corrupted

This MR should be merged after slapos.core has been upgraded 

/reviewed-on nexedi/slapos!115

/reviewed-on nexedi/slapos!117