[SPARK-7432] [MLLIB] disable cv doctest
[SPARK-7432] [MLLIB] disable cv doctest

Temporarily disable flaky doctest for CrossValidator. jkbradley

Author: Xiangrui Meng <9616cf314f60cbadfd3d5d51110130ad7923defb@databricks.com>

Closes #5962 from mengxr/disable-pyspark-cv-test and squashes the following commits:

5db7e5b [Xiangrui Meng] disable cv doctest

(cherry picked from commit 773aa25252f29ca25dbb1ee495b530557fe79405)
Signed-off-by: Xiangrui Meng <9616cf314f60cbadfd3d5d51110130ad7923defb@databricks.com>

andrewor14/iolap,andrewor14/iolap,andrewor14/iolap,andrewor14/iolap,andrewor14/iolap,andrewor14/iolap,andrewor14/iolap