Fix scalastyle warnings in yarn alpha

Author: witgo <witgo@qq.com>

Closes #884 from witgo/scalastyle and squashes the following commits:

4b08ae4 [witgo] Fix scalastyle warnings in yarn alpha
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 '&&'