enable sharding of bok-choy tests
add shard_1 flags to cms bok-choy tests
use paver commands in jenkins script
updated doctring to explain the bok-choy shards
adding discussion tests to shard_1
Merge pull request #4593 from edx/clytwynec/shard_out_bokchoy_tests

Clytwynec/shard out bokchoy tests