Concurrent Ruby: Stop assuming a version number is available where we expect it to be about newrelic-ruby-agent

[workato-integration]

https://new-relic.atlassian.net/browse/NR-232908

[fallwith]

Here's the relevant observed newrelic_agent.log message:

DEBUG : Using auto configuration value for concurrent_ruby to configure instrumentation
ERROR : Error while detecting concurrent_ruby:
ERROR : NameError: uninitialized constant Concurrent::VERSION
DEBUG : Debugging backtrace:
$HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/new_relic/agent/instrumentation/concurrent_ruby.rb:14:in `block (2 levels) in <top (required)>'
  $HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/new_relic/dependency_detection.rb:126:in `block in check_dependencies'
  $HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/new_relic/dependency_detection.rb:124:in `each'
  $HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/new_relic/dependency_detection.rb:124:in `all?'
  $HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/new_relic/dependency_detection.rb:124:in `check_dependencies'
  $HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/new_relic/dependency_detection.rb:64:in `dependencies_satisfied?'
  $HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/new_relic/dependency_detection.rb:28:in `block in detect!'
  $HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/new_relic/dependency_detection.rb:27:in `each'
  $HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/new_relic/dependency_detection.rb:27:in `detect!'
  $HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/new_relic/control/instrumentation.rb:64:in `_install_instrumentation'
  $HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/new_relic/control/instrumentation.rb:47:in `install_instrumentation'
  $HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/new_relic/control/private_instance_methods.rb:39:in `init_instrumentation'
  $HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/new_relic/control/instance_methods.rb:75:in `init_plugin'
  $HOME/.asdf/installs/ruby/2.5.7/lib/ruby/gems/2.5.0/gems/newrelic_rpm-9.7.1/lib/newrelic_rpm.rb:40:in `<top (required)>'

[fallwith]

The version constant Concurrent::VERSION exists in the oldest available version of the gem, v0.7.0. So this doesn't appear to be a version issue.

[fallwith]

We don't have a repro, but #2466 is a bit more paranoid with an extra defined? check.