add -r support to setup.py

setup.py

@@ -227,7 +227,14 @@ def _parse_requirements_file(requirements_file):
     with open(requirements_file) as rfh:
         for line in rfh.readlines():
             line = line.strip()
-            if not line or line.startswith(("#", "-r")):
+            if not line or line.startswith("#"):
+                continue
+            if line.startswith("-r"):
+                file = line.split()[1]
+                ret_requirements = _parse_requirements_file(
+                    os.path.join(os.path.dirname(requirements_file), file)
+                )
+                parsed_requirements.extend(ret_requirements)
                 continue
             if IS_WINDOWS_PLATFORM:
                 if "libcloud" in line: