[SPARK-4946] [CORE] Using AkkaUtils.askWithReply in MapOutputTracker.askTracker to reduce the chance of the communicating problem

Using AkkaUtils.askWithReply in MapOutputTracker.askTracker to reduce the chance of the communicating problem

Author: YanTangZhai <hakeemzhai@tencent.com>
Author: yantangzhai <tyz0303@163.com>

Closes #3785 from YanTangZhai/SPARK-4946 and squashes the following commits:

9ca6541 [yantangzhai] [SPARK-4946] [CORE] Using AkkaUtils.askWithReply in MapOutputTracker.askTracker to reduce the chance of the communicating problem
e4c2c0a [YanTangZhai] Merge pull request #15 from apache/master
718afeb [YanTangZhai] Merge pull request #12 from apache/master
6e643f8 [YanTangZhai] Merge pull request #11 from apache/master
e249846 [YanTangZhai] Merge pull request #10 from apache/master
d26d982 [YanTangZhai] Merge pull request #9 from apache/master
76d4027 [YanTangZhai] Merge pull request #8 from apache/master
03b62b0 [YanTangZhai] Merge pull request #7 from apache/master
8a00106 [YanTangZhai] Merge pull request #6 from apache/master
cbcba66 [YanTangZhai] Merge pull request #3 from apache/master
cdef539 [YanTangZhai] Merge pull request #1 from apache/master
[Minor] Fix a typo of type parameter in JavaUtils.scala

In JavaUtils.scala, thare is a typo of type parameter. In addition, the type information is removed at the time of compile by erasure.

This issue is really minor so I don't  file in JIRA.

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #3789 from sarutak/fix-typo-in-javautils and squashes the following commits:

e20193d [Kousuke Saruta] Fixed a typo of type parameter
82bc5d9 [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into fix-typo-in-javautils
99f6f63 [Kousuke Saruta] Fixed a typo of type parameter in JavaUtils.scala