[SPARK-8776] Increase the default MaxPermSize

I am increasing the perm gen size to 256m.

https://issues.apache.org/jira/browse/SPARK-8776

Author: Yin Huai <yhuai@databricks.com>

Closes #7196 from yhuai/SPARK-8776 and squashes the following commits:

60901b4 [Yin Huai] Fix test.
d44b713 [Yin Huai] Make sparkShell and hiveConsole use 256m PermGen size.
30aaf8e [Yin Huai] Increase the default PermGen size to 256m.