... and normL2.
Add test cases to insufficient unit test for `normL1` and `normL2`.

Ref: https://github.com/apache/spark/pull/5359

Author: lewuathe <lewuathe@me.com>

Closes #5374 from Lewuathe/SPARK-6720 and squashes the following commits:

5541b24 [lewuathe] More accurate tests
dc5718c [lewuathe] [SPARK-6720] PySpark MultivariateStatisticalSummary unit test for normL1 and normL2