Slaprunner: dont run runner-import/runner-export/pbs-push if the space is full on runner1/runner0/runner1 respectively

This fixes part of resiliency tests

/reviewed-on nexedi/slapos!262

( because  allow-picked-versions require all versions to be pinned )

Since erp5 commit "[taskdistribution] Drop needless TaskDistributionTool"
the tool is not available anymore and only TaskDistributor shall be used

It provides fix to call correct endpoints (Distributor instead of a Tool).

/reviewed-on nexedi/slapos!260

See also https://bugs.debian.org/882329

Issue was:
- user project_user was created
- project_user create stored routines
- mysql data is dumped (including list of users)
- mysql data is restored, but stored routines have the information
  DEFINER that must match an existing user. This does not
  work if there is no flush privileges instructions

So make sure to insert flush privileges while dumping

This reproduces what happens on a Prod system, where
TokuDB turned out to use much more CPU than FileStorage.

  If the person wants to use slapos master, it makes no sense provide diferent options

There's little hope that it gets maintained because it contains a C extension whereas alternatives often use ctypes. In particular, it has no support for Python 3, and this is a blocker for us. At the beginning, [I though we were switching to pyinotify](0bb405fc): it is quite popular, and even used by fail2ban, but the code is ugly (big, crazy API, limited, and probably slow).

I didn't really know inotify and it's disappointing to see that created files (CREATE+WRITE+CLOSE_WRITE) can't be distinguished from hard links (CREATE). Acting upon new inodes is a common scenario and in the first case, you want to wait CLOSE_WRITE or you would read a partially written file. What I mean is that inotify is often unreliable, unless you detect changes done by your own software (e.g. you can make sure that files aren't hard-linked) but then some other IPC is probably simpler.

In any case, I open this MR because I haven't tested it. I only checked with pylint (hence the second commit).

/cc @alain.takoudjou @gabriel @luke (from Git history)

/reviewed-on nexedi/slapos!257

inotifyx does not support Python 3.

It was reverted in commit 9c672830
but it is still required to bootstrap from old SlapOS setups.

Replace dropbear by openssh.
Use same rdiff-backup than provided by PBS.
Allow to directly use an IPV6 address with a custom port.