benchmark: clean up common.js
benchmark: clean up common.js

This commit cleans up `benchmark/common.js` with a few generic changes
such as the following:

- declare all `require()`'d libraries at the top instead of in the
  middle
- add some empty whitespace where it helps readability
- changes ambiguous variable names
- standardizes most if / else blocks
- missing semicolons

PR-URL: https://github.com/iojs/io.js/pull/662
Reviewed-By: Nicu Micleușanu <7ba6b26002a178c6e17098ff478119ed69b20e64@gmail.com>
Reviewed-By: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>
Reviewed-By: Stephen Belanger <d033e22ae348aeb5660fc2140aec35850c4da997@stephenbelanger.com>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node