Moving window of keys used by robustness

[serathius]

What would you like to be added?

Currently robustness tests just use a static range of keys key0-key9. During the test we execute different types of writing operations like PUT and DELETE. To make linearization faster we use the fact that PUTs are unique due to unique saved value, however this doesn't work for DELETE. To make DELETE unique at least partially we could make the key window slowly shift. For example, when during the traffic generation delete key0, we could shift the window up to be key1 - key10. This way we could increase the chance that key will be deleted only once.

Why is this needed?

Make deletes unique, removing a need to treat them differently than put.

[serathius]

/cc @henrybear327 @nwnt @fuweid @joshjms

[joshjms]

I'd love to take this

/assign