Updates to docker build script

[dbuddhir]

Few minor changes I made as I faced issues building ranger on my Mac.

• Redirect error on image deletion to null
• update apache mirror url
• update gpg key server

[chitralverma]

@dbuddhir I'm getting the following error on my machine, any ideas on this?

Successfully built 6a22a7db2d3e
Successfully tagged ranger_dev:latest
+ docker run --rm -v /Users/chitralverma/IdeaProjects/ranger:/ranger -w /ranger -v /Users/chitralverma/.m2:/.m2 --name ranger_build ranger_dev mvn -Pall -DskipTests=true clean compile package install
+ '[' mvn = mvn ']'
++ stat -c %u pom.xml
stat: cannot stat 'pom.xml': No such file or directory
+ usermod -u builder
usermod: invalid user ID 'builder'
+ gosu builder bash -c 'ln -sf /.m2 $HOME'
+ exec gosu builder mvn -Pall -DskipTests=true clean compile package install
OpenJDK 64-Bit Server VM warning: ignoring option MaxPermSize=512m; support was removed in 8.0
[ERROR] Could not create local repository at /home/builder/.m2/repository -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/LocalRepositoryNotAccessibleException

I'm on a mac machine and and I'm running the command bash build_ranger_using_docker.sh in the root of the ranger clone directory.

[chitralverma]

Also, FYI, https://issues.apache.org/jira/browse/RANGER-3310 https://github.com/apache/ranger/pull/103