title: Boto3 API for EMR doesn't support 'OnDemandPrice'
body: <p>Having some trouble with creating an EMR spark cluster using <code>Boto3</code>. The error I'm getting is as follows:</p>
  <pre><code>botocore.exceptions.ClientError: An error occurred (ValidationException) when calling the RunJobFlow operation: Attempted to set bid price for on demand instance group.
  </code></pre>
  <p>I specified this configuration as follows:</p>
  <pre><code> 'Name': 'Core - 2',
   'InstanceRole': 'CORE',
   'InstanceType': 'i3.2xlarge',
   'InstanceCount': 50,
   'BidPrice': 'OnDemandPrice',
  </code></pre>
  <p>It seems the <code>Boto3</code> API doesn't allow this and I don't want to use the AWS Cli either. Is there a workaround to specify spot instances through <code>Boto3</code>?</p>