[SPARK-19373][MESOS] Base spark.scheduler.minRegisteredResourceRatio …

…on registered cores rather than accepted cores

See JIRA

Unit tests, Mesos/Spark integration tests

cc skonto susanxhuynh

Author: Michael Gummelt <mgummeltmesosphere.io>

Closes #17045 from mgummelt/SPARK-19373-registered-resources.

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Author: Michael Gummelt <mgummelt@mesosphere.io>

Closes #17129 from mgummelt/SPARK-19373-registered-resources-2.1.