Merge branch 'bwh/fix-git-remote-name-check-1.4' into 'bst-1.4'

git source plugin: Fix check for remote existence

See merge request BuildStream/buildstream!2031
diff --git a/buildstream/plugins/sources/git.py b/buildstream/plugins/sources/git.py
index 4952464..94472ba 100644
--- a/buildstream/plugins/sources/git.py
+++ b/buildstream/plugins/sources/git.py
@@ -185,7 +185,7 @@
                 fail="Failed to retrieve list of remotes in {}".format(self.mirror),
                 cwd=self.mirror
             )
-            if remote_name not in remotes:
+            if remote_name not in remotes.strip().split():
                 self.source.call(
                     [self.source.host_git, 'remote', 'add', remote_name, url],
                     fail="Failed to add remote {} with url {}".format(remote_name, url),