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 nexedi/slapos!693

Typos and fix of description, was wrongly copy&pasted from master.

We don't want to build against system library that might or might not be
present on the host.

This also cause SR test to fail with:

    RuntimeError: ./parts/trafficserver7/bin/traffic_manager uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/bin/traffic_crashlog uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/bin/traffic_server uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/bin/traffic_ctl uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/bin/traffic_logstats uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/bin/traffic_via uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/bin/traffic_cop uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/bin/traffic_layout uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/bin/traffic_logcat uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/lib/libtsutil.so.7.1.6 uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/lib/libtsmgmt.so.7.1.6 uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/lib/libtsmgmt.so.7 uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/lib/libtsmgmt.so uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/lib/libtsutil.so.7 uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2
    ./parts/trafficserver7/lib/libtsutil.so uses system library /lib/x86_64-linux-gnu/libcap.so.2 for libcap.so.2

/reviewed-on nexedi/slapos!691

This reverts commit d57770ac,
and adds 2 patches from Debian.