info: Fix seperator when superproject revision is "None"

Not seen when using sp.commit_id since it has a trailing newline,
so modify def commit_id to strip the stdout and append a newline
for both using the helper.

Manifest groups: default,platform-linux
Superproject revision: None----------------------------

->

Manifest groups: default,platform-linux
Superproject revision: None
----------------------------

Test: repo info -o with and without superproject
Change-Id: I06ad4dd1f7b64b5374c343e583c8a2690dc9c6e7

git_superproject.py

@@ -151,7 +151,7 @@ class Superproject:
                 p.stderr,
             )
             return None
-        return p.stdout
+        return p.stdout.strip()
 
     @property
     def project_commit_ids(self):

subcmds/info.py

@@ -106,6 +106,7 @@ class Info(PagedCommand):
         srev = sp.commit_id if sp and sp.commit_id else "None"
         self.heading("Superproject revision: ")
         self.headtext(srev)
+        self.out.nl()
 
         self.printSeparator()