We need to access six when calling the 'replicated.replicate' macro.

"max" and "int" became directly accessible in slapos.recipe.template.

Taken from development.cfg

Not sure if this is ok

check-maximum-elapsed-time and failure-amount are added to support
monitoring distant backends with some margin on the failures.

This fixes errors like:

    File "python3.6/lib/python3.6/re.py", line 142, in <module>
      class RegexFlag(enum.IntFlag):
  AttributeError: module 'enum' has no attribute 'IntFlag

hexagonit.recipe.download-1.7.post4 (Nexedi's patch) is not compatible
with Python 3 (yet?).

In order to avoid the very long #!/.../python path, call surykatka with
explicit interpreter.

By default one failure is considered as bad thing, but allows to select sites
which shall be treated with some tolerance.

Allows to configure maximum time for which the site is considered correct.

For each class (the maximum elapsed time value) separate surykatka process
is started, in order to not impact fast sites checking by long timeouts on
slow sites.

Improvements:

 * reports on elapsed_time
 * timeout handling fixed
 * reporting filtering fixed

pysvn 1.7.10 already supports Python 3, but this patch did not.

/reviewed-on !693