[Spark] RDD take() method: overestimate too much

In the comment (Line 1083), it says: "Otherwise, interpolate the number of partitions we need to try, but overestimate it by 50%."

`(1.5 * num * partsScanned / buf.size).toInt` is the guess of "num of total partitions needed". In every iteration, we should consider the increment `(1.5 * num * partsScanned / buf.size).toInt - partsScanned`
Existing implementation 'exponentially' grows `partsScanned ` ( roughly: `x_{n+1} >= (1.5 + 1) x_n`)

This could be a performance problem. (unless this is the intended behavior)


In bad case that buf.size = 1, num = 1000, partsScanned = 1, then numPartsToTry will be 1000, so it's better to use partsScanned * 4 as the upper boundary of numPartsToTry.