Behave should not collide with step names

[boolafish]

in our integration tests, there are several steps in different feature share the same name. eg. userA deposit 1 eth to plasma, userA transfers 1 eth to userB.

They should be using the same implementation. Currently there are multiple implementation for the same step name. However, behave framework does not ensures that which implementation it would take. see: behave/behave#496.
Though luckily it worked in our CI, but It breaks in my local env.

Here's my screenshot:

You can see it is calling challenge_spent_coin_flow.feature:3 first but calling challenge_double_spending_flow.py:26 later.

[boolafish]

Currently it is hard to re-use the integration step code because those hard coded block numbers that client need. if our CI does not break too much might worth wait a bit for #71. Or we can just re-name all steps in different features as a work-around now.