[fuchsia] handle relative paths in local-sdk.py

Change-Id: I420d0c5c4b37ed9eb0d56d8251f83ffcac372d07
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1696269
Reviewed-by: Fabrice de Gans-Riberi <fdegans@chromium.org>
Reviewed-by: James Robinson <jamesr@chromium.org>
Commit-Queue: James Robinson <jamesr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676645}

tools/fuchsia/local-sdk.py

@@ -64,7 +64,7 @@ def main(args):
   EnsureEmptyDir(output_dir)
 
   original_dir = os.getcwd()
-  fuchsia_root = args[0]
+  fuchsia_root = os.path.abspath(args[0])
   merged_manifest = None
   manifest_parts = set()