Cfncluster

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* Fix a bug in `cfncluster configure` introduced in 1.6.0

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* Refactor scaling up to take into account the number of pending/requested jobs/slots and instance slots.
* Refactor scaling down to scale down faster and take advantage of per-second billing.
* Add `scaledown_idletime` parameter as part of scale-down refactoring
* Lock hosts before termination to ensure removal of dead compute nodes from host list
* Fix HTTP proxy support

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* Add option to disable ganglia `extra_json = { "cfncluster" : { "ganglia_enabled" : "no" } }`
* Fix `cfncluster update` bug
* Set SGE Accounting summary to be true, this reports a single accounting record for a mpi job
* Upgrade cfncluster-node to Boto3

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* Add support for GovCloud, us-gov-west-1 region

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* feature:``cfncluster``: Added ClusterUser as a stack output. This makes it easier to get the username of the head node.
* feature:``cfncluster``: Added `cfncluster ssh cluster_name`, this allows you to easily ssh into your clusters. It allows arbitrary command execution and extra ssh flags to be provided after the command. See https://cfncluster.readthedocs.io/en/latest/commands.htmlssh
* change:``cfncluster``: Moved global cli flags to the command specific flags. For example `cfncluster --region us-east-1 create` now becomes `cfncluster create --region us-east-1`
* bugfix:``cfncluster-cookbook``: Fix bug that prevented c5d/m5d instances from working
* bugfix:``cfncluster-cookbook``: Set CPU as a consumable resource in slurm
* bugfix:``cfncluster-node``: Fixed Slurm behavior to add CPU slots so multiple jobs can be scheduled on a single node

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* change:``cfncluster``: Added "ec2:DescribeVolumes" permissions to
CfnClusterInstancePolicy
* change:``cfncluster``: Removed YAML CloudFormation template, it can be
generated by the https://github.com/awslabs/aws-cfn-template-flip tool

* updates:``cfncluster``: Add support for eu-west-3 region

* feature:``cfncluster-cookbook``: Added parameter to specify custom
cfncluster-node package

* bugfix:``cfncluster``: Fix --template-url command line parameter
* bugfix:``cfncluster-cookbook``: Poll on EBS Volume attachment status
* bugfix:``cfncluster-cookbook``: Fixed SLURM cron job to publish pending
metric
* bugfix:``cfncluster-node``: Fixed Torque behaviour when scaling up from an
empty cluster