pass sample rate in the sample_rate parameter

Hello,

Sample rate is being passed into increment as a delta (the second parameter). It should be passed in as sample_rate (the third parameter)

This pull request passes to increment a delta of 1 (default value) and the supplied sample rate (as the 3rd parameter)

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Alternative solution:

make statsd_count_success (et all) have parameters more consistent with increment
OLD: method, name, sample_rate
PROPOSED: method, name, delta, sample_rate


I can fix pull request if you like the alternative solution better

Thanks,
Keenan