Remove extra semicolon in Task.scala

Author: GuoQiang Li <witgo@qq.com>

Closes #1876 from witgo/remove_semicolon_in_Task_scala and squashes the following commits:

c6ea732 [GuoQiang Li] Remove extra semicolon in Task.scala
[SPARK-2950] Add gc time and shuffle write time to JobLogger

The JobLogger is very useful for performing offline performance profiling of Spark jobs. GC Time and Shuffle Write time are available in TaskMetrics but are currently missed from the JobLogger output. This patch adds these two fields.

~~Since this is a small change, I didn't create a JIRA. Let me know if I should do that.~~

cc kayousterhout

Author: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

Closes #1869 from shivaram/job-logger and squashes the following commits:

1b709fc [Shivaram Venkataraman] Add a space before GC_TIME
c418105 [Shivaram Venkataraman] Add gc time and shuffle write time to JobLogger
[SPARK-2898] [PySpark] fix bugs in deamon.py

1. do not use signal handler for SIGCHILD, it's easy to cause deadlock
2. handle EINTR during accept()
3. pass errno into JVM
4. handle EAGAIN during fork()

Now, it can pass 50k tasks tests in 180 seconds.

Author: Davies Liu <davies.liu@gmail.com>

Closes #1842 from davies/qa and squashes the following commits:

f0ea451 [Davies Liu] fix lint
03a2e8c [Davies Liu] cleanup dead children every seconds
32cb829 [Davies Liu] fix lint
0cd0817 [Davies Liu] fix bugs in deamon.py