Drone speedup (#2588)

Drone speedup (#2588)

* Start switchind test to custom Docker images

Using Docker images with pre-installed delendencies will speedup
testing.

* Debug build in drone.io

* Use variable instead hardcoded path to the source

* Debug variable substitution by drone

Also according to comments in code DRONE_WORKSPACE is deprecated and
CI_WORKSPACE is a new form.

* One more try to use variables.

It looks like drone uses same rules as docker-compose:
https://docs.docker.com/compose/compose-file/#variable-substitution

* Cleanup debug

* Less verbose make output

* Be consistent in variable escaping

It works without escaping only becuse ${VAR} currently expanded by
drone, but $VAR is not.

* Use alpine base image for nodejs

It is smaller.

* Return rspamd-test

* Revert variable escaping

Wihtout escaping it is more easy to copy-past command for testing.
Just don't use ${var} when var should be expanded by shell and not
drone.

* Add debug

* Fix yaml parsing error

* Fix exit code capture

It should be done on the same line, because drone insert 'echo + cmd'
between commands.

* Remove debug

* Readability

No functional changes.

* Return functional tests

* Be consistent

* Add git stub for coveralls

* Send coverage

* Fix yaml parsing error

* Add links to Dockerfiles

* Send test log in case of test failure

XXX if rspamd-test failed, but functional was successful robot log will be
attached (but not useful).

* Don't run rspamd-test and functional tests in parallel

It looks like there is a race condition in writing coverage files.

* Try to run tests in parallel

* Add debug

* Fix parallel test run

test/rspamd-test and functional test both use luacov.stats.out file
in current directory. Run ./rspamd-test from anther directory.

* Use drone condition for sending coveralls report

Also don't send report if empty tocken was provided.

* Add mininal python3 compatibility