Customizable remote repository url for hive versions unit test

When the VersionSuite test runs from sql/hive it downloads different versions from hive.

Unfortunately the IsolatedClientClassloader (which is used by the VersionSuite) uses hardcoded fix repositories:

    val classpath = quietly {
      SparkSubmitUtils.resolveMavenCoordinates(
        hiveArtifacts.mkString(","),
        SparkSubmitUtils.buildIvySettings(
          Some("http://www.datanucleus.org/downloads/maven2"),
          ivyPath),
        exclusions = version.exclusions)
    }

The problem is with the hard-coded repositories:

1. it's hard to run unit tests in an environment where only one internal maven repository is available (and central/datanucleus is not)

2. it's impossible to run unit tests against custom built hive/hadoop artifacts (which are not available from the central repository)

VersionSuite has already a specific SPARK_VERSIONS_SUITE_IVY_PATH environment variable to define a custom local repository as ivy cache.

I suggest to add an additional environment variable (SPARK_VERSIONS_SUITE_IVY_REPOSITORIES to the HiveClientBuilder.scala), to make it possible adding new remote repositories for testing the different hive versions.