modules.pip editable to handle use case with local module w/o egg.

ref #3751, #2052

* Update pip's regex for detecting egg's (https://github.com/pypa/pip/blob/develop/pip/req.py#L1402) from editable.find('egg').
* Use `startswith` to detect if local file. Note that `pip install -e` will handle the use case of `file://` and `/` paths itself.

Only raise the exception if it's non local (vcs) and egg not found.