setup: fix usage of deprecated get_script_header()

For now we catch the AttributeError and use the new
function if the deprecated function does not exist
so that we don't break older versions.

setup.py

@@ -63,7 +63,12 @@ def run(self):
         # replaced by the correct interpreter. We do the same here.
         bs_cmd = self.get_finalized_command('build_scripts')
         executable = getattr(bs_cmd, 'executable', easy_install.sys_executable)
-        script = easy_install.get_script_header("", executable) + SCRIPT_TMPL
+        try:
+            script = easy_install.get_script_header(
+                "", executable) + SCRIPT_TMPL
+        except AttributeError:
+            script = easy_install.ScriptWriter.get_header(
+                "", executable) + SCRIPT_TMPL
         if PY3:
             script = script.encode('ascii')
         self.write_script("gnocchi-api", script, 'b')
@@ -74,7 +79,10 @@ def install_wrapper_scripts(self, dist):
         develop.develop.install_wrapper_scripts(self, dist)
         if self.exclude_scripts:
             return
-        script = easy_install.get_script_header("") + SCRIPT_TMPL
+        try:
+            script = easy_install.get_script_header("") + SCRIPT_TMPL
+        except AttributeError:
+            script = easy_install.ScriptWriter.get_header("") + SCRIPT_TMPL
         if PY3:
             script = script.encode('ascii')
         self.write_script("gnocchi-api", script, 'b')