[test failure: master] LogStash::Agent metrics after config reloading when reloading a good config increases the successful reload count

FAILURE elastic/logstash#master f06e859 multijob-unix-compatibility/os=debian - 20170816162731-F3E45E0A

https://logstash-ci.elastic.co/job/elastic+logstash+master+multijob-unix-compatibility/os=debian/94/console

```
Failures:

1) LogStash::Agent metrics after config reloading when reloading a good config increases the successful reload count
Failure/Error: sleep(0.01) while ::File.read(new_file).chomp.empty?

Timeout::Error:
execution expired
# /var/lib/jenkins/workspace/elastic+logstash+master+multijob-unix-compatibility/os/debian/logstash-core/spec/logstash/agent_spec.rb:375:in `block in (root)'
# /var/lib/jenkins/workspace/elastic+logstash+master+multijob-unix-compatibility/os/debian/logstash-core/spec/logstash/agent_spec.rb:374:in `block in (root)'
# /var/lib/jenkins/workspace/elastic+logstash+master+multijob-unix-compatibility/os/debian/vendor/bundle/jruby/2.3.0/gems/rspec-wait-0.0.9/lib/rspec/wait.rb:46:in `block in /var/lib/jenkins/workspace/elastic+logstash+master+multijob-unix-compatibility/os/debian/vendor/bundle/jruby/2.3.0/gems/rspec-wait-0.0.9/lib/rspec/wait.rb'
# /var/lib/jenkins/workspace/elastic+logstash+master+multijob-unix-compatibility/os/debian/lib/bootstrap/rspec.rb:13:in `'
# ------------------
# --- Caused by: ---
# (anonymous error class):
# execution expired
# /var/lib/jenkins/workspace/elastic+logstash+master+multijob-unix-compatibility/os/debian/logstash-core/spec/logstash/agent_spec.rb:375:in `block in (root)'

Finished in 9 minutes 12 seconds (files took 18.89 seconds to load)
2311 examples, 1 failure, 3 pending

Failed examples:

rspec /var/lib/jenkins/workspace/elastic+logstash+master+multijob-unix-compatibility/os/debian/logstash-core/spec/logstash/agent_spec.rb:396 # LogStash::Agent metrics after config reloading when reloading a good config increases the successful reload count

Randomized with seed 31957
```