Merge remote-tracking branch 'origin/pr/74' into v4

Closes #74.
update broken hadoop link
update Maven link
Merge pull request #78 from nchammas/broken-links

Update Apache download links
Support Spark 1.1.1
Merge pull request #81 from andrewor14/patch-1

Support Spark 1.1.1
Adding Spark 1.2.0
Merge pull request #83 from pwendell/v4

Adding Spark 1.2.0
Add realpath to fix rJava install issues
Add realpath to create_image.sh
Merge pull request #84 from shivaram/v4-realpath

Add realpath to fix rJava install issues
Merge pull request #3 from mesos/v4

merge upstream changes
Add in new Packer scripts.
Try waiting on yum locks.
Ignore Packer logs.
Packer-generated AMIs.
Add in benchmark of new AMIs without Spark.
remove release-specific builds
install and use GNU parallel with rsync