SPARK-1925: Replace '&' with '&&'

JIRA: https://issues.apache.org/jira/browse/SPARK-1925

Author: zsxwing <zsxwing@gmail.com>

Closes #879 from zsxwing/SPARK-1925 and squashes the following commits:

5cf5a6d [zsxwing] SPARK-1925: Replace '&' with '&&'

(cherry picked from commit cb7fe5034826844f1b50fbe8b92646317b66f21c)
Signed-off-by: Reynold Xin <rxin@apache.org>