Make missing global config dir not fatal in tempest init

Due to the complexities and inability of the python packaging
infrastructure to install data files properly or consistently we have
to be prepared for the case when we have no idea where the data files
end up from a tempest install. Thus this commit makes tempest init
not fail when it can't find the global config dir and just logs a
warning that it couldn't be found.

Change-Id: Iff944092228ca1ae081e8faaf10ee0048e7ea414
diff --git a/tempest/cmd/init.py b/tempest/cmd/init.py
index 633b9e9..dc28777 100644
--- a/tempest/cmd/init.py
+++ b/tempest/cmd/init.py
@@ -114,15 +114,22 @@
             config_parse.write(conf_file)
 
     def copy_config(self, etc_dir, config_dir):
-        shutil.copytree(config_dir, etc_dir)
+        if os.path.isdir(config_dir):
+            shutil.copytree(config_dir, etc_dir)
+        else:
+            LOG.warning("Global config dir %s can't be found" % config_dir)
 
     def generate_sample_config(self, local_dir, config_dir):
-        conf_generator = os.path.join(config_dir,
-                                      'config-generator.tempest.conf')
+        if os.path.isdir(config_dir):
+            conf_generator = os.path.join(config_dir,
+                                          'config-generator.tempest.conf')
 
-        subprocess.call(['oslo-config-generator', '--config-file',
-                         conf_generator],
-                        cwd=local_dir)
+            subprocess.call(['oslo-config-generator', '--config-file',
+                             conf_generator],
+                            cwd=local_dir)
+        else:
+            LOG.warning("Skipping sample config generation because global "
+                        "config dir %s can't be found" % config_dir)
 
     def create_working_dir(self, local_dir, config_dir):
         # Create local dir if missing