Add a cli flag to specify the amount of storage

[KolbyML]

@acolytec3 @ScottyPoi ping to see.

I am looking to add Portal-Hive tests for missing edge cases, both Trin and Fluffy already support a flag like this. I am not sure if Ultralight has a storage limit yet, but a flag would be nice cause then you can simulate what happens when storage gets low.