Factor out almost all fs. and path. calls in the tool

This will be useful when we want to be smart with windows file paths later
Also, all of the file calls are asynchronous with fibers now, which comes with
many benefits.

This is a combination of 23 commits. Original messages:
Wrap a large number of fs calls inside files.*

Convert a few more fs calls to files.*

More moving fs.* to files

Implement read/write streams and open/read/close

Get rid of fs from auth.js

Remove fs and unused imports from catalog-local and catalog-remote

Remove unused imports from catalog.js

Replace a whole lot of fs calls

Fix error

Migrate a lot more fs. calls to files.

Add a temporary symlink method

Convert old test to files.*

Use files.pathX instead of path.x everywhere

Replace path.x to files.pathX in tests

Small fixes to files.js and one rename

Make cleanup run in a fiber

Make wrapping functions take function name in case we need it

Add some timeouts and stuff to HCP tests

wrapFsFunc also makes a sync version of the function

Sometimes you just don't want to yield!

Make sure JsImage readFromDisk doesn't yield

Remove unused imports from npm test

Change order of test now that some things don't yield

Fix missing files import, and add a debug error printout
Add comment explaining existsSync
Fix broken code for dos2unix absolute path conversion
Always convert arguments to an array
Merge pull request #3295 from meteor/fs-refactor

Factor out almost all fs. and path. calls in the tool