CI: bring back integration testing

[kares]

the pub-sub integration spec is disabled since it posts a new status to twitter and is currently broken.
the (previously disabled) other suite does a bunch of 'functional' plugin use-cases including reading through a proxy.

NOTE: assumes twitter auth credentials to be set on the CI env ✔️

The proxied twitter connection still failing:

logstash_1_e91759c60e18 | [2020-10-07T18:48:29,712][WARN ][logstash.inputs.twitter  ] Twitter client error {:message=>"End of file reached", :exception=>EOFError, :backtrace=>["org/jruby/RubyIO.java:2889:in `readpartial'", "/usr/share/logstash/vendor/jruby/lib/ruby/gems/shared/gems/twitter-6.2.0/lib/twitter/streaming/connection.rb:19:in `stream'", "/usr/share/logstash/vendor/jruby/lib/ruby/gems/shared/gems/twitter-6.2.0/lib/twitter/streaming/client.rb:119:in `request'", "/usr/share/logstash/vendor/jruby/lib/ruby/gems/shared/gems/twitter-6.2.0/lib/twitter/streaming/client.rb:38:in `filter'", "/usr/share/plugins/plugin/lib/logstash/inputs/twitter.rb:151:in `do_run'", "/usr/share/plugins/plugin/lib/logstash/inputs/twitter.rb:131:in `run'", "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:378:in `inputworker'", "/usr/share/logstash/logstash-core/lib/logstash/java_pipeline.rb:369:in `block in start_input'"], :options=>nil}