Extract Askari::HBaseEnvironment.load!

This sets up the java classpath to bring in the hbase jars.

Also deal with a subtle hbase dependency bug. Apparently requiring in
slf4j or hbase's patched junit can, depending the order tests are run,
cause classloader/search problems.  Since neither library appears
necessary, we simply skip loading them.

Other hbase classpath entries are normalized with `File.expand_path`.
The normalization should help make our tests more robust across
platforms (i.e. hbase classpath has different species of oddities on
linux vs osx.)