Add PEP8 and general lint conformance to in-house scripts

My intent in this diff was mostly style linting, so I disabled
non-stylistic pylint linters that fired in the interests of making this
a sane diff with one purpose: stylistic consistency and conformance. If
I disabled them it means they were thrown somewhere and should probably
be looked into some time :-)

This diff adds:
- PEP8 conformance (tested with pep8)
- A cleanup of stuff shown by `pylint`, with quite a few linters
  disabled. See above for rationale to disable these -- in the end this
  was mostly unused variables, unused imports, etc). These are the
  linters I disabled:
  - attribute-defined-outside-init
  - bad-classmethod-argument
  - bare-except
  - broad-except
  - exec-used
  - invalid-name
  - logging-not-lazy
  - method-hidden
  - missing-docstring
  - redefined-outer-name
  - too-few-public-methods
  - too-many-instance-attributes
  - too-many-locals
  - unused-argument
- flake8 warnings fixed (warnings were about redefinition of previous
  variables in a listcomp)

I didn't do anything with git-clang-format since it's from an external
project and it's possible that there may be a wish to merge it in again
later if it gets updated upstream, but you could, of course, apply this
to that script as well if you so wish. Right now it's not at all PEP8
conformant.
Revert removal of unused symbols in genapi per @theopolis' comment:

At https://github.com/cdown/osquery/commit/2a93de#commitcomment-8583208:
> Although the removed symbols aren't referenced in this script they are
> used in the spec evaluation.
Merge pull request #431 from cdown/its_lintmas

Add PEP8 and general lint conformance to in-house scripts