Misc release script improvements

Signed-off-by: Joffrey F <joffrey@docker.com>

scripts/release.sh

@@ -22,7 +22,15 @@ echo "##> Removing stale build files"
 rm -rf ./build || exit 1
 
 echo "##> Tagging the release as $VERSION"
-git tag $VERSION || exit 1
+git tag $VERSION
+if [[ $? != 0 ]]; then
+    head_commit=$(git show --pretty=format:%H HEAD)
+    tag_commit=$(git show --pretty=format:%H $VERSION)
+    if [[ $head_commit != $tag_commit ]]; then
+        echo "ERROR: tag already exists, but isn't the current HEAD"
+        exit 1
+    fi
+fi
 if  [[ $2 == 'upload' ]]; then
     echo "##> Pushing tag to github"
     git push $GITHUB_REPO $VERSION || exit 1
@@ -30,10 +38,10 @@ fi
 
 
 pandoc -f markdown -t rst README.md -o README.rst || exit 1
+echo "##> sdist & wheel"
+python setup.py sdist bdist_wheel
+
 if [[ $2 == 'upload' ]]; then
-    echo "##> Uploading sdist to pypi"
-    python setup.py sdist bdist_wheel upload
-else
-    echo "##> sdist & wheel"
-    python setup.py sdist bdist_wheel
-fi
+    echo '##> Uploading sdist to pypi'
+    twine upload dist/docker-$VERSION*
+fi
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