Fix incorrect injected USER directive

* CLOUDBLD-4939

This bug was introduced in commit 6140b73.

Signed-off-by: Chenxiong Qi <cqi@redhat.com>

atomic_reactor/plugins/pre_inject_yum_repo.py

@@ -26,7 +26,7 @@ class InjectYumRepoPlugin(PreBuildPlugin):
     def _final_user_line(self):
         user = self._find_final_user()
         if user:
-            return f'USER {user}'
+            return user
 
         builder = self.workflow.builder
         if not builder.dockerfile_images.base_from_scratch:

tests/plugins/test_yum_inject.py

@@ -420,7 +420,51 @@ def test_no_base_image_in_dockerfile(tmpdir):
             RUN rm -f '/etc/yum.repos.d/custom-{}.repo'
             '''),
 
-        ]
+        ],
+
+        # Reset the USER found from the last stage properly.
+        # `USER 1001` should be reset after the removal commands
+        [
+            True, '',
+            [
+                (
+                    'http://repos.host/custom.repo',
+                    dedent('''\
+                    [new-packages]
+                    name=repo1
+                    baseurl=http://repo.host/latest/$basearch/os
+                    '''),
+                    dedent(f'''\
+                    [new-packages]
+                    sslcacert=/tmp/{CA_BUNDLE_PEM}
+                    name=repo1
+                    baseurl=http://repo.host/latest/$basearch/os
+                    '''),
+                ),
+            ],
+            dedent('''\
+            FROM base
+            RUN gcc main.c
+            FROM fedora:33
+            USER 1001
+            WORKDIR /src
+            '''),
+            dedent(f'''\
+            FROM base
+            ADD {CA_BUNDLE_PEM} /tmp/{CA_BUNDLE_PEM}
+            ADD atomic-reactor-repos/* /etc/yum.repos.d/
+            RUN gcc main.c
+            FROM fedora:33
+            ADD {CA_BUNDLE_PEM} /tmp/{CA_BUNDLE_PEM}
+            ADD atomic-reactor-repos/* /etc/yum.repos.d/
+            USER 1001
+            WORKDIR /src
+            USER root
+            RUN rm -f '/etc/yum.repos.d/custom-{{}}.repo'
+            RUN rm -f /tmp/{CA_BUNDLE_PEM}
+            USER 1001
+            '''),
+        ],
     ]
 )
 @responses.activate