Fix development mode test execution

[andsel]

After setting the LOGSTASH_PATH and LOGSTASH_SOURCE to use a local Logstash and running bundle install and exec rspec, it terminates with error:

An error occurred while loading ./spec/inputs/azure_event_hub_spec.rb.
Failure/Error: require "logstash/devutils/rspec/spec_helper"

LoadError:
  load error: jopenssl/load -- java.lang.NoClassDefFoundError: org/jruby/util/io/FileExistsException
# /usr/share/rvm/gems/jruby-9.3.9.0/gems/jruby-openssl-0.9.19-java/lib/openssl.rb:1:in `<main>'
# /usr/share/rvm/gems/jruby-9.3.9.0/gems/logstash-core-5.6.4-java/lib/logstash/patches/stronger_openssl_defaults.rb:2:in `<main>'
# /usr/share/rvm/gems/jruby-9.3.9.0/gems/logstash-core-5.6.4-java/lib/logstash/patches.rb:5:in `<main>'
# /usr/share/rvm/gems/jruby-9.3.9.0/gems/logstash-core-5.6.4-java/lib/logstash/environment.rb:186:in `<main>'
# /usr/share/rvm/gems/jruby-9.3.9.0/gems/logstash-devutils-1.3.6-java/lib/logstash/devutils/rspec/spec_helper.rb:17:in `<main>'
# ./spec/inputs/azure_event_hub_spec.rb:2:in `<main>'
# ------------------
# --- Caused by: ---
# Java::JavaLang::ClassNotFoundException:
#   org.jruby.util.io.FileExistsException
#   java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:476)
No examples found.

How to reproduce:

> export LOGSTASH_PATH=/path/to/logstash_clone && export LOGSTASH_SOURCE=1
> bundle install
> bundle exec rspec

• Relates https://github.com/elastic/logstash/issues/14203