Extended KVM SR does not have this hosts in allowed, and we need to stick
with it.

For reference in case if some existing Python distribution does not install,
it was detected with "git diff 8deeab.. -- stack/slapos.cfg"

The Debian packaging of our RINA kernel builds with GCC 4.9,
which is not available on Stretch:

  # apt install ./linux-build-deps_4.1.33+rina65.g2e1cdbcb4-1_amd64.deb
  ...
  The following packages have unmet dependencies:
  linux-build-deps : Depends: gcc-4.9 but it is not installable

The regexp was matching "slappart10" in `/path/to/slappart10/software.cfg`,
was also matching "slappart10" in `/path/to/aaslappart10aa/software.cfg`
and was not matching "slappart1" in `/path/to/slappart1/software.cfg`
or "slappart1000" in `/path/to/slappart1000/software.cfg`.

The fix allows to match "slappartX" in `/path/to/slappartX/software.cfg`
where X can be between 0 to infinite. Also, it protects from matching
"slappartX" in `/path/to/aaaslappartXaaa/software.cfg`.

Now that the test suite passes again for Jessie, let's try Stretch.

If two NayuOS images are built on the same day, the second one will not get zipped. The -f flag in gzip can be used to overwrite the previous image

/reviewed-on nexedi/slapos!336

This SR was developed and tested in environments where both software and instance where owned by the same unix user. These are fixes for problems discovered when running on a "system level" slapos.

This cannot easily be tested without actually using different users (especially the mistake on the mode of the executable script), but this MR introduce some tests to check that service running in instance does not open files or unix sockets outside of instance. It also introduce a utility method to access the supervisor RPC API, it can be useful if tests needs to start/stop a process or get process PID to inspect this process.

I ran into problems, because proftpd sets [`PR_SET_DUMPABLE`](http://man7.org/linux/man-pages/man2/prctl.2.html) to 0, which disables any possibility of inspecting a running program. See 18e28bbb  for details about the chosen approach.

/cc @rafael @Nicolas @luke @Eteri @vpelletier 

/reviewed-on nexedi/slapos!334

erp5, mariadb: Allow users to set additional environment variables to mysqld to use third party ODBC libraries for CONNECT storage engine.