superproject: Don't update the commit ids of projects if remote is different.

1) Skip setting the revision id (commit id) for the projects whose
   remote doesn't match superproject's remote.
2) exp-superproject/superproject_override.xml includes local_manfiest's
   projects. When we load this XML, don't reload projects from local.xml
   (otherwise we will get duplicate projects errors).

Tested the code with the following commands.

$ ./run_tests -v

+ Test with local.xml
  $ repo_dev init -u sso://android.git.corp.google.com/platform/manifest -b master --use-superproject --partial-clone --clone-filter=blob:limit=10M && mkdir -p .repo/local_manifests && (gcertstatus -quiet=true || gcert) && ln -s /google/src/head/depot/google3/wireless/android/build_tools/aosp/manifests/mirror-aosp-master-with-vendor/local.xml  .repo/local_manifests/local.xml

  $ repo_dev sync -c -j8

+ Test without local.xml
  $ repo_dev init -u sso://android.git.corp.google.com/platform/manifest -b master --partial-clone --clone-filter=blob:limit=10M --repo-rev=main --use-superproject
  $ repo_dev sync -c -j8

Bug: [google internal] b/186395810
Change-Id: I4e9d4ac2d94a9fc0cef0ccd787b6310758009e86
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/304882
Tested-by: Raman Tenneti <rtenneti@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>
diff --git a/manifest_xml.py b/manifest_xml.py
index 64b7fb4..73556a5 100644
--- a/manifest_xml.py
+++ b/manifest_xml.py
@@ -596,6 +596,10 @@
     return set(x.strip() for x in exclude.split(','))
 
   @property
+  def HasLocalManifests(self):
+    return self._load_local_manifests and self.local_manifests
+
+  @property
   def IsMirror(self):
     return self.manifestProject.config.GetBoolean('repo.mirror')