config/module: fix test failures on Windows

When parsing URLs on Windows, assume it is a drive letter path
if the second element is a ':' character. Format the drive letter
path as a "file:///"-path prior to parsing the URL.

Fixes test failures of the following form in command on Windows:

=== RUN TestApply_plan
--- FAIL: TestApply_plan (0.00s)
        apply_test.go:379: bad: 1

		module download not supported for scheme 'c'

config/module/url_helper.go

@@ -9,8 +9,13 @@ import (
 
 func urlParse(rawURL string) (*url.URL, error) {
 	if runtime.GOOS == "windows" {
-		// Make sure we're using "/" on Windows. URLs are "/"-based.
-		rawURL = filepath.ToSlash(rawURL)
+		if len(rawURL) > 1 && rawURL[1] == ':' {
+			// Assume we're dealing with a file path.
+			rawURL = fmtFileURL(rawURL)
+		} else {
+			// Make sure we're using "/" on Windows. URLs are "/"-based.
+			rawURL = filepath.ToSlash(rawURL)
+		}
 	}
 	u, err := url.Parse(rawURL)
 	if err != nil {