Exclude Java agent jars from class path of launching class loader

ExecutableArchiveLauncher creates a ClassLoader that is used by the
Launcher to load an application’s classes. During the creation of this
ClassLoader URLs from another ClassLoader are copied over. This was
resulting in Java agents that are added to the system class loader
via the -javaagent launch option being available on both the system
class loader and the created class loader. Java agents are intended to
always be loaded by the system class loader. Making them available on
another class loader breaks this model.

This commit updates ExecutableArchiveLauncher so that it skips the URLs
of any Java agents (found by examining the JVM’s input arguments) when
copying URLs over to the new classloader, thereby ensuring that Java
agents are only ever loaded by the system class loader.

Fixes #863