Redo warmup fail logic

[dkropachev]

Currently Warmup respects failFast and fails if there is any error in such case.
Let's have separate logic for Warmup, it should look at fail to success percentage and fail if it is greater then warmup-fail-error-rate (implement this option)
Also it can fail by this condition only after warmup-safe-period secods are passed since warmup is started.

[soyacz]

why do we need warmup in Gemini?

[dkropachev]

@soyacz , idea is that when/if cassandra is used we need to warm it up, otherwise - to fillout table with values before doing measurements.
@roydahan , roy, WDYT? do we realy need it there ?

[roydahan]

I don't know if we need it, i'm not sure I understand the scenario you mentioned above.