SPARK-4971: Fix typo in BlockGenerator comment

Author: CodingCat <zhunansjtu@gmail.com>

Closes #3807 from CodingCat/new_branch and squashes the following commits:

5167f01 [CodingCat] fix typo in the comment

(cherry picked from commit fda4331d58aae454a2b0f4c757d105f8bc228a3d)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>
[SPARK-3787][BUILD] Assembly jar name is wrong when we build with sbt omitting -Dhadoop.version

This PR is another solution for When we build with sbt with profile for hadoop and without property for hadoop version like:

    sbt/sbt -Phadoop-2.2 assembly

jar name is always used default version (1.0.4).

When we build with maven with same condition for sbt, default version for each profile is used.
For instance, if we  build like:

    mvn -Phadoop-2.2 package

jar name is used hadoop2.2.0 as a default version of hadoop-2.2.

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

Closes #3046 from sarutak/fix-assembly-jarname-2 and squashes the following commits:

41ef90e [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into fix-assembly-jarname-2
50c8676 [Kousuke Saruta] Merge branch 'fix-assembly-jarname-2' of github.com:sarutak/spark into fix-assembly-jarname-2
52a1cd2 [Kousuke Saruta] Fixed comflicts
dd30768 [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into fix-assembly-jarname2
f1c90bb [Kousuke Saruta] Fixed SparkBuild.scala in order to read `hadoop.version` property from pom.xml
af6b100 [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into fix-assembly-jarname
c81806b [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into fix-assembly-jarname
ad1f96e [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into fix-assembly-jarname
b2318eb [Kousuke Saruta] Merge branch 'master' of git://git.apache.org/spark into fix-assembly-jarname
5fc1259 [Kousuke Saruta] Fixed typo.
eebbb7d [Kousuke Saruta] Fixed wrong jar name
HOTFIX: Slight tweak on previous commit.

Meant to merge this in when committing SPARK-3787.
[SPARK-4952][Core]Handle ConcurrentModificationExceptions in SparkEnv.environmentDetails

Author: GuoQiang Li <witgo@qq.com>

Closes #3788 from witgo/SPARK-4952 and squashes the following commits:

d903529 [GuoQiang Li] Handle ConcurrentModificationExceptions in SparkEnv.environmentDetails

(cherry picked from commit 080ceb771a1e6b9f844cfd4f1baa01133c106888)
Signed-off-by: Patrick Wendell <pwendell@gmail.com>