Update shark-env.sh.template
Update shark-env.sh.template

Explain that MESOS_NATIVE_LIBRARY is only for Mesos clusters.
alabid/blinkdb,amplab/shark,lzshlzsh/shark,mattyb149/blinkdb,sameeragarwal/blinkdb,sjyk/sampleclean,mapr/shark,mapr/shark,sameeragarwal/blinkdb,lzshlzsh/shark,mattyb149/blinkdb,alabid/blinkdb,alabid/blinkdb,amplab/shark,mattyb149/blinkdb,sjyk/sampleclean,mapr/shark,lzshlzsh/shark,sameeragarwal/blinkdb,amplab/shark,sjyk/sampleclean