PARQUET-507: Reduce the runtime of rle-test
PARQUET-507: Reduce the runtime of rle-test

I twiddled this a bit to cut the runtime in half. I'd like to reduce it further but looking for feedback -- my preference would be to use system entropy (`std::random_device`) to seed the PRNG and print the seed on failure. So we could run far fewer tests (e.g. only 50 or 100 or so) and occasionally run into flakiness or failure if we refactor and break something internally. Thoughts?

Author: Wes McKinney <wes@cloudera.com>

Closes #37 from wesm/PARQUET-507 and squashes the following commits:

d75f2ed [Wes McKinney] Tidying per comments
0ed951a [Wes McKinney] Buglet
ba97491 [Wes McKinney] Further shorten random tests; use device entropy and print random seed on failure
a357dd1 [Wes McKinney] Preallocate vector in BitRle.Random and run half as many iterations

Change-Id: I8454ada4337cf98793294632e14ebe96f73c5111

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