Older Spark Version Required, ARM Template Fails on Spark pool creation

[mdowns75]

Hi. It should be noted that you must deploy spark version 2.4 in order for this to work properly. Alternatively, the ARM template deployment could be fixed to properly deploy the spark pool and either set the "dynamically allocate executors" to "disabled" or keep "enable" and set the "Default number of executors" values. Currently the spark deployment in the ARM template fails. If the ARM template is fixed, ensure 2.4 spark version is set