Get and Set Config for OSS Index, IQ Server

[DarthHater]

Last week much to my chagrin I discovered a few things:

• Nancy currently has no way of specifying OSS Index config, which means it's hard to escape rate limiting if you run in to it!
• I never built the ability to use a persistent config for IQ Server!

This pull request makes the following changes:

• Adds set.go to package configuration and wires up to it in main.go for nancy config. Methods made public so that cheque and ahab can consume them easily as well
  • Config is saved to ~ and then .ossindex or .iqserver, and as .oss-index-config or .iq-server-config to be consistent with other tools out of the DevEx factory (set once, picked up by the other tools, great success)
• Adds an ability to loadConfigFromFile to parse.go, which we really should refactor at some point (there is so much duplication it's making me go ahhhhhhh, but not doing that in this PR quite yet)
• Chunks up ossindex.go so that I can pass in configuration a bit easier. Also decomposes some larger methods into smaller ones. Adds a new public function of AuditPackageWithOSSIndex, so that if someone is currently using AuditPackages upstream, they can still do that. Add's a deprecation notice to AuditPackages with a note to use the new function instead.
• Adds tests for saving config, and verifying it was saved properly

Couple lil fly by improvements:

• LogLady now truncates when it opens the log file, ensuring the log file is only ever for the most recent use of nancy, noticed this while helping on #107
• Passes a better error when you are rate limited, which explains how to get an OSS Index account and set your config

cc @bhamail / @DarthHater / @zendern / @fitzoh

[DarthHater]

@zendern let er rip. I had NEVER tested something that took stdin input before, fun learning experiment doing so. Tests pass, and confirm that something is written to disk. I can think of one nice thing to do which is to not use /tmp like I am and use ioutils.TempFile, figured I'd see if you had any other ideas there though!

[DarthHater]

I believe I covered all the bases now. Parse tests now set ConfigLocation to a nonsensical place so they won't test loading config from file. Previously if you'd set your config locally you'd get failing tests from it loading.

As well, I changed the logger to truncate the file by default now, which is effectively poor person log rotation. This was not specific to this task, but was easy and I figured I'd do it to make my own testing a bit easier.

I've tested the config for OSS Index and IQ Server myself locally, and everything checks out!