Bug 1626104 - Change mach lint --config-path to be relative to topsrcdir. r=linter-reviewers,ahal

This makes the --config-path option relative to topsrcdir rather then the current
directory.
Using a relative path is difficult for a developer running mach lint locally as
the command has to change as the working directory changes. A stable base path also
facilitates creating an alias in machrc.

Differential Revision: https://phabricator.services.mozilla.com/D68909

--HG--
extra : moz-landing-system : lando

python/mozlint/mozlint/cli.py

@@ -204,6 +204,9 @@ def run(paths, linters, formats, outgoing, workdir, rev, edit,
     from mozlint import LintRoller, formatters
     from mozlint.editor import edit_issues
 
+    lintargs['config_paths'] = [os.path.join(lintargs['root'], p) for p in
+                                lintargs['config_paths']]
+
     if list_linters:
         lint_paths = find_linters(lintargs['config_paths'], linters)
         linters = [os.path.splitext(os.path.basename(l))[0] for l in lint_paths]