add support for new GRID GPU g2.2xlarge (non-GPGPU) instance type
volume: fix for reporting duplicate vol hosts
node: fix deprecation warnings from sshutils
cluster: raise error if MOUNT_PATH=/
static: move g2.2xlarge into CLUSTER_GPU_TYPES
Merge branch 'feature-grid-gpu-types' into develop

closes gh-319
Merge branch 'develop' of https://github.com/jtriley/StarCluster into develop