Allowable values for --ebs-volume-type should state "standard (magnetic) | io1 | gp2 | sc1 | st1"

[rjhintz]

Change ec2_server_create.rb

 option :ebs_volume_type,
        :long => "--ebs-volume-type TYPE",
        :description => "Standard or Provisioned (io1) IOPS or General Purpose (gp2)",
        :proc => Proc.new { |key| Chef::Config[:knife][:ebs_volume_type] = key },
        :default => "standard"

to:

 option :ebs_volume_type,
        :long => "--ebs-volume-type TYPE",
        :description => "standard (magnetic) | io1 | gp2 | sc1 | st1",
        :proc => Proc.new { |key| Chef::Config[:knife][:ebs_volume_type] = key },
        :default => "standard"

to align with AWS CLI run-instances.

This assumes the AWS EBS disk type abbreviations such as gp2 are generally understood.

Default value should also be changed from standard (magnetic) to gp2 (SSD) to align with current AWS practice. However, this is a disruptive change for current code. I'll propose this separately.

See also #451. I have to do the prerequisite admin to do a PR, but didn't want this to get lost.

[dheerajd-msys]

@rjhintz Thanks for your comments. We will get it fixed soon.

[rjhintz]

Ok, thanks. I couldn't figure out how to do a PR because the method for becoming a contributor seems obsolete. See #452

[NimishaS]

Fixed in #464