code-coverage: add option to ignore errors on missing files

- Add options to ignore errors on genthml at the merge
stage for missing source code files.

Signed-off-by: Saul Romero <saul.romero@arm.com>
diff --git a/coverage-tool/coverage-reporting/clone_sources.py b/coverage-tool/coverage-reporting/clone_sources.py
index ec38acd..99c80ab 100644
--- a/coverage-tool/coverage-reporting/clone_sources.py
+++ b/coverage-tool/coverage-reporting/clone_sources.py
@@ -71,6 +71,7 @@
                     print(("WARNING!: Mismatch in git repo {}\nExpected {}, "
                            "Cloned {}").format(source['URL'], source['COMMIT'],
                                                commit_id))
+                    return True
         elif source['type'] == "http":
             if handler is not None:
                 return handler(source,
@@ -124,7 +125,7 @@
                 url = git["URL"]
                 commit_id = git["COMMIT"]
                 output_loc = os.path.join(output_dir, git["LOCATION"])
-                cmd = "git clone {} {}".format(url, output_loc)
+                cmd = "rm -rf {1} || true;git clone {0} {1}".format(url, output_loc)
                 output = call_cmd(cmd)
                 if git['REFSPEC']:
                     call_cmd("cd {};git fetch -q origin {}".format(