SparkSubmit with Ivy jars is very slow to load with no internet access

Spark Submit adds maven central & spark bintray to the ChainResolver before it adds any external resolvers.

https://github.com/apache/spark/blob/branch-1.4/core/src/main/scala/org/apache/spark/deploy/SparkSubmit.scala#L821

When running on a cluster without internet access, this means the spark shell takes forever to launch as it tries these two remote repos before the ones specified in the --repositories list. In our case we have a proxy which the cluster can access it and supply it via --repositories.

This is also a problem for users who maintain a proxy for maven/ivy repos with something like Nexus/Artifactory. Having a repo proxy is popular at many organisations so I'd say this would be a useful change for these users as well. In the current state even if a maven central proxy is supplied, it will still try and hit central.

I see two options for a fix;

• Change the order repos are added to the ChainResolver, making the --repositories supplied repos come before anything else. https://github.com/apache/spark/blob/branch-1.4/core/src/main/scala/org/apache/spark/deploy/SparkSubmit.scala#L843
• Have a config option (like spark.jars.ivy.useDefaultRemoteRepos, default true) which when false wont add the maven central & bintry to the ChainResolver.

Happy to do a PR for this fix.