Allow user to pass command-line arguments to kernel

[xkjyeah]

The Scala kernel accepts command line arguments, such as --profile, --ip, --default-repositories. It also supports passing settings to the Scala compiler, e.g. -- -Xmax-classfile-name 170 (the last one in particular is very useful when running Toree from inside Docker images or on encrypted volumes).

This patch allows users to pass command line arguments to the kernel via:

jupyter toree install \
  --kernel-opts="-- -Xmax-classfile-name 170" \
  --interpreters=Scala,PySpark,SparkR,SQL

Not sure if kernel_opts is the best name though. kernel_extra_opts may be better since --profile is already being passed to the kernel.