Bigtop-3070 support Spark Thrift Server in Charm

[buggtb]

The thrift server has no exposure and should be configurable for Spark SQL support etc.

[kwmonroe]

One other thing @buggtb, since this opens a new port, we'll need 10000 listed in layer.yaml:

https://github.com/apache/bigtop/blob/master/bigtop-packages/src/charm/spark/layer-spark/layer.yaml#L25

As well as a check for spark_enable_thriftserver in the start method to know if we should run hookenv.open_port, similar to what we do for opening the spark-master-ui port:

https://github.com/apache/bigtop/blob/master/bigtop-packages/src/charm/spark/layer-spark/lib/charms/layer/bigtop_spark.py#L377