Handle broken FileDescriptorGaugeSet in Java 9

[gimaker]

FileDescriptorGaugeSet is broken at least in OpenJDK 9, throwing an exception
like this:

java.lang.reflect.InaccessibleObjectException: Unable to make public long com.sun.management.internal.OperatingSystemImpl.getOpenFileDescriptorCount() accessible: module jdk.management does not "opens com.sun.management.internal" to unnamed module @1a451d4d
	at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:337)
	at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:281)
	at java.base/java.lang.reflect.Method.checkCanSetAccessible(Method.java:198)
	at java.base/java.lang.reflect.Method.setAccessible(Method.java:192)
	at com.codahale.metrics.jvm.FileDescriptorRatioGauge.invoke(FileDescriptorRatioGauge.java:48)
	at com.codahale.metrics.jvm.FileDescriptorRatioGauge.getRatio(FileDescriptorRatioGauge.java:35)
	at com.codahale.metrics.RatioGauge.getValue(RatioGauge.java:64)
	at com.spotify.metrics.jvm.FileDescriptorGaugeSet$1.getValue(FileDescriptorGaugeSet.java:54)
	at com.spotify.metrics.ffwd.FastForwardReporter.reportGauge(FastForwardReporter.java:231)
	at com.spotify.metrics.ffwd.FastForwardReporter.report(FastForwardReporter.java:193)
	at com.spotify.metrics.ffwd.FastForwardReporter.report(FastForwardReporter.java:181)
	at com.spotify.metrics.ffwd.FastForwardReporter$2.run(FastForwardReporter.java:348)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:514)
	at java.base/java.util.concurrent.FutureTask.runAndReset(FutureTask.java:305)
	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:300)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
	at java.base/java.lang.Thread.run(Thread.java:844)

Any metrics that would have been reported AFTER this metric will not be reported
at all, which is pretty bad - no rates, etc would be reported when this throws.

Until upstream (ideally codahale metrics, possibly semantic-metrics) is patched
to handle this properly we reimplement the FileDescriptorSetGauge from
semantic-metrics in a way that handles this safely.

[gimaker]

@jhaals @tommyulfsparre

[codecov-io]

Codecov Report

Merging #231 into 1.x will decrease coverage by 0.03%.
The diff coverage is 63.63%.

@@             Coverage Diff              @@
##                1.x     #231      +/-   ##
============================================
- Coverage     69.66%   69.63%   -0.04%     
  Complexity      653      653              
============================================
  Files           139      139              
  Lines          2924     2934      +10     
  Branches        172      172              
============================================
+ Hits           2037     2043       +6     
- Misses          844      848       +4     
  Partials         43       43

Impacted Files	Coverage Δ	Complexity Δ
...java/com/spotify/apollo/metrics/MetricsModule.java	55.81% <63.63%> (+1.26%)	5 <0> (ø)	⬇️

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[jhaals]

👍

[mattnworb]

Can you report this in https://github.com/dropwizard/metrics/issues too? I searched and didn't see anything.