Allowed LoadGeneratorFramework to read password from a file.

Review: https://reviews.apache.org/r/23695
Made LoadGeneratorFramework a check program instead of a bin program.

Review: https://reviews.apache.org/r/23696
Fixed a memory leak in limiter.hpp.

Review: https://reviews.apache.org/r/23916
Add missing whitespace to coverage script

Review: https://reviews.apache.org/r/23934