Cast for new jmxfetch

[ive]

In current dadadog 4.x version if yaml (for example tomcat) has option port: set as "12345" (note " instead of just pure number), datadog read config, start jmxfetch but
$datadog-agent info shows
Unexpected exception while initiating instance localhost:11198 : java.lang.String cannot be cast to java.lang.Integer
java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer
at org.datadog.jmxfetch.Connection.(Connection.java:49)
at org.datadog.jmxfetch.ConnectionManager.getConnection(ConnectionManager.java:43)
at org.datadog.jmxfetch.Instance.init(Instance.java:81)
at org.datadog.jmxfetch.App.init(App.java:298)
at org.datadog.jmxfetch.App.init(App.java:208)
at org.datadog.jmxfetch.App.main(App.java:53)

Previous version behave differently. It seems wize to try casting port to int() or log error\warning.

[remh]

Closed in favor of:
DataDog/jmxfetch#16