Ignore clone-depth attribute when fetching to a mirror

If a manifest includes projects with a clone-depth=1 attribute, and a
workspace is initialised from that manifest using the --mirror option,
any workspaces initialised and synced from the mirror will fail with:

  fatal: attempt to fetch/clone from a shallow repository

on the projects that had the clone-depth.

Ignore the clone-depth attribute when fetching from the remote to a
mirror workspace. Thus the mirror will be synched with a complete
clone of all the repositories.

Change-Id: I638b77e4894f5eda137d31fa6358eec53cf4654a
diff --git a/project.py b/project.py
index 48fa82b..876b86a 100644
--- a/project.py
+++ b/project.py
@@ -1683,11 +1683,17 @@
 
     is_sha1 = False
     tag_name = None
+    depth = None
 
-    if self.clone_depth:
-      depth = self.clone_depth
-    else:
-      depth = self.manifest.manifestProject.config.GetString('repo.depth')
+    # The depth should not be used when fetching to a mirror because
+    # it will result in a shallow repository that cannot be cloned or
+    # fetched from.
+    if not self.manifest.IsMirror:
+      if self.clone_depth:
+        depth = self.clone_depth
+      else:
+        depth = self.manifest.manifestProject.config.GetString('repo.depth')
+
     if depth:
       current_branch_only = True