Enable H2O embedding in target containers (in this case Spark worker
node)

Most of containers keep system classpath clean without application
specific jars. Hence, we need to look for resources not only at system
class path (which is standalone setup), but also via context classloader
of current thread (which is method used by containers).
Modify weaver pool to look for classes not only via system
classloader but also via Weaver classloader (which can be different and
configured by target container).