Reenable assembly of the Hadoop2 zipfile

In 5306e9eb78ef573c7d87327d9cef33775efb3873, I accidentally disabled
the assembly plugin titan-dist/titan-dist-hadoop-2/pom.xml when
running `mvn clean install -Paurelius-release`. Forgot that declaring
a profile on the command line in Maven, like -Paurelius-release,
silently disables all other profiles that would normally be activated
by default if -P hadn't been given.