[SPARK-9490] [DOCS] [MLLIB] MLlib evaluation metrics guide example python code uses deprecated print statement

Use print(x) not print x for Python 3 in eval examples
CC sethah mengxr -- just wanted to close this out before 1.5

Author: Sean Owen <sowen@cloudera.com>

Closes #7822 from srowen/SPARK-9490 and squashes the following commits:

01abeba [Sean Owen] Change "print x" to "print(x)" in the rest of the docs too
bd7f7fb [Sean Owen] Use print(x) not print x for Python 3 in eval examples