Upgrade to opentracing-java 0.21.0

[objectiser]

and handle PEER_PORT change from short to int

[CLAassistant]

All committers have signed the CLA.

[codecov-io]

Codecov Report

Merging #137 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #137      +/-   ##
============================================
+ Coverage     35.96%   35.99%   +0.03%     
- Complexity      587      589       +2     
============================================
  Files            87       93       +6     
  Lines          6298     6301       +3     
  Branches       1046     1046              
============================================
+ Hits           2265     2268       +3     
- Misses         3852     3854       +2     
+ Partials        181      179       -2

Impacted Files	Coverage Δ	Complexity Δ
...r/jaeger/httpclient/TracingRequestInterceptor.java	84.61% <100%> (ø)	5 <0> (ø)	⬇️
...ain/java/com/uber/jaeger/context/TracingUtils.java	50% <0%> (-5.56%)	2% <0%> (-3%)
...m/uber/jaeger/httpclient/ClientRequestCarrier.java	83.33% <0%> (ø)	2% <0%> (-2%)	⬇️
...ain/java/com/uber/jaeger/metrics/StatsFactory.java
...er/jaeger/filters/jaxrs2/ClientRequestCarrier.java	83.33% <0%> (ø)	2% <0%> (?)
...a/com/uber/jaeger/filters/jaxrs2/TracingUtils.java	60% <0%> (ø)	3% <0%> (?)
.../java/com/uber/jaeger/dropwizard/StatsFactory.java	100% <0%> (ø)	4% <0%> (?)
...java/com/uber/jaeger/filters/jaxrs2/Constants.java	0% <0%> (ø)	0% <0%> (?)
...-core/src/main/java/com/uber/jaeger/Constants.java	0% <0%> (ø)	0% <0%> (?)
...java/com/uber/jaeger/dropwizard/Configuration.java	50% <0%> (ø)	3% <0%> (?)
... and 3 more

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[objectiser]

This update was required to enable Jaeger's java Tracer to be used with the Apache Camel camel-example-opentracing example.

[pavolloffay]

Could you please do release of 0.18.0 once this is merged?