Send coverage report to analysers

[oparoz]

In the scrutinizer config, in tools, add:

    external_code_coverage:
        timeout: 3600 # Timeout in seconds. 60 minutes

In drone, add a post test command

  - wget https://scrutinizer-ci.com/ocular.phar
  - php ocular.phar code-coverage:upload --format=php-clover tests/_output/coverage.xml
  - bash <(curl -s https://codecov.io/bash) -f tests/_output/coverage.xml -t ff710fa8-260c-4a61-bdd3-0771d6aea5b5

In the Readme, add

[![Code Coverage](https://scrutinizer-ci.com/g/nextcloud/circles/badges/coverage.png?b=master)](https://scrutinizer-ci.com/g/nextcloud/circles/?branch=master)

Documentation

https://docs.codecov.io/docs/about-the-codecov-bash-uploader

[ArtificialOwl]

we will use codecov only