Allow block device mapping
Added description to blockdevicemapping in clusterspec and filter out only ephemeral drives for volume mapping.
Use JSON to parse block device mapping string.
Updated clusterspec description of block device mapping
Substitute regex matching for OR chain.
Made suggested changes. Exposed "mapping map" on clusterspec. Moved ec2 specific stuff to bootstraptemplate
made suggested changes.
Removed JSON format for passing blockdevicemapping
Updated cluster spec help text
Merge pull request #7 from rescale/enable-block-device-mapping

Allow block device mapping