fix(net-rc,cwd): adds more robust netrc parsing and cwd detection

[justinwilaby]

fixes #134
fixes #135

This PR addresses 2 edge cases:

1. a non-encrypted .netrc file which contains strange whitespace - this was reported by 1 user
2. A better detection for the cwd passed to the child process for CLI execution

Testing

These are edge cases and cannot be easily tested. Testing the above is limited to verifying no regressions are introduced.

1. Make sure sign in/sign out still works
2. Make sure you can link at least 1 app to the workspace.

W-17969497
W-17969515

[sbosio]

Looks good. I tested and both log-in and heroku git commands worked perfectly when linking a workspace with an app.