Adding Dummy benchmark scenarios

Added Dummy benchmark scenario with methods dummy and
dummy_exception and the their task docs. The link to the
trello card is:
https://trello.com/c/vB3VpR1d/191-add-dummy-benchmark-scenario

Change-Id: I25df9356e0f6b703b1ba5428a5c98d386c6dde10
Merge "Adding Dummy benchmark scenarios"