[SPARK-3193]output errer info when Process exit code is not zero in test suite

https://issues.apache.org/jira/browse/SPARK-3193
I noticed that sometimes pr tests failed due to the Process exitcode != 0,refer to
https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/18688/consoleFull
https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/19118/consoleFull

[info] SparkSubmitSuite:
[info] - prints usage on empty input
[info] - prints usage with only --help
[info] - prints error with unrecognized options
[info] - handle binary specified but not class
[info] - handles arguments with --key=val
[info] - handles arguments to user program
[info] - handles arguments to user program with name collision
[info] - handles YARN cluster mode
[info] - handles YARN client mode
[info] - handles standalone cluster mode
[info] - handles standalone client mode
[info] - handles mesos client mode
[info] - handles confs with flag equivalents
[info] - launch simple application with spark-submit *** FAILED ***
[info]   org.apache.spark.SparkException: Process List(./bin/spark-submit, --class, org.apache.spark.deploy.SimpleApplicationTest, --name, testApp, --master, local, file:/tmp/1408854098404-0/testJar-1408854098404.jar) exited with code 1
[info]   at org.apache.spark.util.Utils$.executeAndGetOutput(Utils.scala:872)
[info]   at org.apache.spark.deploy.SparkSubmitSuite.runSparkSubmit(SparkSubmitSuite.scala:311)
[info]   at org.apache.spark.deploy.SparkSubmitSuite$$anonfun$14.apply$mcV$sp(SparkSubmitSuite.scala:291)
[info]   at org.apache.spark.deploy.SparkSubmitSuite$$anonfun$14.apply(SparkSubmitSuite.scala:284)
[info]   at org.apacSpark assembly has been built with Hive, including Datanucleus jars on classpath

this PR output the process error info when failed, it can be helpful for diagnosis.

Author: scwf <wangfei1@huawei.com>

Closes #2108 from scwf/output-test-error-info and squashes the following commits:

0c48082 [scwf] minor fix according to comments
563fde1 [scwf] output errer info when Process exitcode not zero
Minor - Fix trivial compilation warnings.

Author: Prashant Sharma <prashant.s@imaginea.com>

Closes #2331 from ScrapCodes/compilation-warn and squashes the following commits:

44c1e76 [Prashant Sharma] Minor - Fix trivial compilation warnings.