Merge log4j helper with hbase helper, overhaul class loading.

This appears to fix both helpers.  log4j apparently was suffering from
a load order problem, while the hbase jar loading was plain wrong.

The hbase classloading issues were being masked by our test_classpath
file generated from maven.  In fact, with the hbase helper working,
test_classpath is now unnecessary.  It has been removed.

You might notice we don't explicitly test that the hbase jars appear
in $LOADED_FEATURES after load!ing.  Turns out testing that robustly
is a lot harder than it looks.  Compound this with the fact that
travis appears to be doing something fishy with zookeeper jar
symlinks.  Anyway, we satisfy ourselves with loading a few HBase
classes in the test.