Fix crash in get_all_stats() if arr is empty

Should fix jtriley/StarCluster#339.
Added compression option to ssh/scp
sshutils: fix port initialization bug

Fix originally contributed by @ebrevdo
Merge branch 'feature-ssh-compression' into develop

closes gh-294
use upstream scp module from @jbardin

StarCluster's scp module originally came from:

https://github.com/jbardin/scp.py

before it was packaged nicely on PyPI. All of StarCluster's scp
improvements have been committed upstream (along with a few bug fixes)
and released in the 0.7.0 version of scp on pypi:

http://pypi.python.org/pypi/scp

Removed StarCluster's internal copy of scp in favor of declaring scp as
an official dependency.

closes gh-331
Merge branch 'use-scp-on-pypi' into develop

closes gh-331
listinstances: show vpc_id and subnet_id
node: use Node.addr property in Node.shell

Avoids trying to SSH to the private ip address of a VPC instance in the
case that the instance is in publicly available subnet with an elastic
ip. This patch simply switches to using Node.addr property rather than
reimplementing the logic in Node.shell.
awsutils: fix group traffic auth in create_group

Removed the cidr_ip kwarg and added the src_group_group_id kwarg to all
authorize_security_group calls when auth_group_traffic=True. Avoids
opening up all ports to the world for both VPC and non-VPC groups. This
issue was introduced by the recent VPC merge - it does not exist in the
latest stable release (0.94.3).

closes gh-341
cluster: store subnet_id in cluster group tags

Otherwise addnode fails due to subnet_id not being restored by
Cluster.load_receipt and consequently not passed to
EasyEC2.request_instances which results in the following error:

InvalidParameterCombination: VPC security groups may not be used for a
non-VPC launch

closes gh-342
listclusters: show private ip if no pub ip for VPC
Merge pull request #340 from liffiton/patch-1
ebsimage: log the ebs volume formatting step

This prevents users from thinking the ebsimage command has stalled when
using it on an instance-store instance. In this case the ebsimage
command has to attach and format a volume and then sync the root file
system which is a lengthy process. The lack of info message for the
formatting step leaves users in the dark while the format takes place.
Added an info message and also set silent=False when running mkfs.ext3
and rsync so that users are more aware of what's happening.

closes gh-334
image: fix for bmap when converting s3->ebs

Pass instance_store=True to EasyEC2.create_block_device_map when
converting instance-store AMIs to EBS-backed. Otherwise any instances
created from the resulting AMI will fail to boot due to block device map
issues.
image: reduce rsync output by switching -v to -q
awsutils: dont specify ephemeral drives w/ t1.micro

Stumbled upon this brand new error this morning when simply launching a
t1.micro test cluster:

UnsupportedOperation: Block device mappings of ephemeral volumes are not
supported for the instance type 't1.micro'.

This patch fixes the error.
image: set fs label = / on root vol (s3->ebs)
awsutils: clear account attr cache if region changes

Updated EasyEC2's support_platforms and default_vpc properties to wipe
the cache and refetch the account attributes if the current region
doesn't match the region from the last fetch.
spothistory: use classic or vpc prices based on default vpc

Updated EasyEC2.get_spot_history to either show VPC or EC2-classic spot
prices based on whether or not the user has a default vpc. If the user
does have a default VPC then the default spot prices are VPC otherwise
it defaults to EC2-classic prices. Also added vpc=False and
classic=False kwargs to EasyEC2.get_spot_history which forces the
function to return prices for a given platform regardless of whether or
not the user has a default VPC.
spothistory: add --vpc and --classic options

Added these options to allow the user to override the spot price
platform autodetection that occurs based on whether or not the user has
a default VPC. These options are mutually exclusive.