Running Jepsen tests in TeamCity

@martinmr: thanks for the writeup.

@Paras: a full jepsen run takes about 7 hrs: https://teamcity.dgraph.io/buildConfiguration/Dgraph_Jepsen?state=successful and it would make sense to run it once a day

@joaquin: do we have any provision to get alerted if a nightly test fails? would it be simple to enable an option for weekly tests? Could be an option for the load/stress tests that we are running on a adhoc basis