Add work-around for wrong version of commons-codec being included

The FindBugs plugin, through Jenkins remoting, using a method of commons-codec that exists only in v1.4 (or later).  Jenkins remoting v2.20 or earlier included commons-codec v1.4, so swarm-client-jar-with-dependencies.jar included this as a transitive dependency.

With remoting v2.21 and later, this dependency was removed.  "By chance" swarm-plugin includes a transitive dependency on commons-codec, but this is for v1.2.  Therefore, commons-codec is included in swarm-client-jar-with-dependencies.jar but with the wrong version.  This causes the FindBugs plugin to fail due to the NoSuchMethodException being thrown.

This patch fixes this problem by making the commons-codec dependency explicit; although I consider this a work-around.  I think the real problem lies between FindBugs plugin and remoting.