[SPARK-2550][MLLIB][APACHE SPARK] Support regularization and intercept in pyspark's linear methods

Related to Jira Issue: [SPARK-2550](https://issues.apache.org/jira/browse/SPARK-2550?jql=project%20%3D%20SPARK%20AND%20resolution%20%3D%20Unresolved%20AND%20priority%20%3D%20Major%20ORDER%20BY%20key%20DESC)
Xiangrui suggested to keep Scala code as simple as possible and only to throw the `IllegalArgumentException` from there. I tried with pattern matching and by creating enumerations however the result was complicated and I ended up adding more classes to the scala and to python code.