without failing the overall pipeline.

This reverts commit d970e1e7b4.

It is broken and I don't know how to fix it.

 - Fix more deprecated Robot Framework syntax
 - Remove log following
 - Remove some artefacts in teardown
 - Restore use of demjson

It can be useful to know if stack usage will be too high.

If was removed in:
03eabb4c57

Drone 0.8 and Drone 1.x are not fully compatible.

Different perltidy versions format code differently.

and embedded styles

It is mostly redundant.

It turned out that clang significantly slower than gcc on rspamd code
(at least with -O0). Switch off torch to decrease build time.

Build clang plugin and use it to check rspamd printf-like functions
(rspamd_printf, rspamd_fprintf, rspamd_default_log_function, e.t.c).

Compilation with -O2/-O3 is slow.

luacov-coveralls merge mode (-j flag) was created to join reports
containing coverage for different source files (e.g. C and Lua code).
Coverage for the same file in two report is not merged, instead one
source file is added several times to source_files array in JSON. As
a result if we use luacov-coveralls -j on report for same source files
it ends up spending a lot of time on parsing and dumping big JSON files.

This change reduces functional test time from 7+ minutes to 4+ minutes.

Remove all but the last failing keyword inside `BuiltIn.Wait Until
Keyword Succeeds` to reduce amount of useless information in robot log.

Remove all but the last failing keyword inside `BuiltIn.Wait Until
Keyword Succeeds` to reduse amount of useless inforamtion in robot log.

* pagination is disabled by --batch
* use options order like in gdb docs

With indentation block literal is not folded as expected.

It is not currently used.

Sending functional test log (about 5Mb) in a email attachmend was temporary
solution.
Upload them to https://ci.rspamd.com/testlogs/ instead.
Link to log/report will be printed in build log.

Don't run gdb yet, it requires more work and can be done when it will be
needed.

* Add utility to prepare C coverage for upload to coveralls.io

It turned out that it is more easy to write own script then debug
and fix coveralls utility (https://github.com/eddyxu/cpp-coveralls).

gcov-coveralls.py can be used as a replacement for coveralls.

* Save coverage data from .gcda files only once

Coverage data in .gcda files is merged after each binary invocation,
so we can run all test and then gather coverage data.

If we dump them two times execution counts will be more then they be.

* Switch from coveralls (cpp-coveralls) to own script

Problem with coveralls was, that coverage for source files outside build
directory was not added to the report.

* Add tool to dump info from json for coveralls.io

* Add debug

* Fix: don't die if there is no service_job_id in json

* Debug

* Fix dump_coveralls.py

* Rename to gcov_coveralls.py (s/-/_/)

For most files in this repo '_' is used as separator.

* Don't add source code to coveralls JSON

According to https://docs.coveralls.io/api-introduction
Coverals don't need source code, only MD5 digest to tracks changes.

Anyway source code is already added by luacov-coveralls and source_digest
is added by cpp-coveralls and gcov_coveralls.py
Both options seems to work for now.

* Provide path to source directory to merge_coveralls.py

merge_coveralls.py has code to filter files and remove prefixes.
When --root points to source directory merge_coveralls.py can strip
prefix from absolute path in JSONs generated by luacov-coveralls.

* Style

Don't add parameters with default values.

* Make --output optional

It useful mainly for debugging. We can send report without saving it.

* Log CI_COMMIT_AUTHOR env var

It is not clear from drone.io source how CI_COMMIT_AUTHOR variable is
set. Log it to see what it means.

* Move merge_coveralls.py to test/tools

This script is used not only for funcional test coverage, but for
rspamd-test coverage too.

* Remove debug

* Style

Use more compact formatting.

* Write comment about parallel tests running [SKIP CI]

Document why running tests in parallel may be bad idea (but still do so).

* Fix typo [SKIP CI]

Based on analagous check added to CircleCI:
9ace1e0519