Fix the SparkEnv null pointer exception in shark-shell.
Fix the SparkEnv null pointer exception in shark-shell.

mapr/shark,alabid/blinkdb,vax11780/shark,mapr/shark,alabid/blinkdb,amplab/shark,sameeragarwal/blinkdb,lzshlzsh/shark,lzshlzsh/shark,alabid/blinkdb,sjyk/sampleclean,sjyk/sampleclean,mattyb149/blinkdb,sjyk/sampleclean,vax11780/shark,mapr/shark,sameeragarwal/blinkdb,sameeragarwal/blinkdb_dev,mattyb149/blinkdb,sameeragarwal/blinkdb,sameeragarwal/blinkdb_dev,sameeragarwal/blinkdb_dev,amplab/shark,mattyb149/blinkdb,lzshlzsh/shark,amplab/shark,vax11780/shark