transform ca_path getter to property

ca_manager.py

@@ -46,18 +46,20 @@ class CAManager(object):
     def db_path(self):
         return os.path.join(self.path, 'ca_manager.db')
 
-    def _get_ssh_cas_dir(self):
+    @property
+    def ssh_ca_dir(self):
         return os.path.join(self.path, 'ssh_cas')
 
     def _get_ssh_ca_path(self, ca_id):
-        cas_dir = self._get_ssh_cas_dir()
+        cas_dir = self.ssh_ca_dir
         return os.path.join(cas_dir, ca_id)
 
-    def _get_ssl_cas_dir(self):
+    @property
+    def ssl_ca_dir(self):
         return os.path.join(self.path, 'ssl_cas')
 
     def _get_ssl_ca_path(self, ca_id):
-        cas_dir = self._get_ssl_cas_dir()
+        cas_dir = self.ssl_ca_dir
         return os.path.join(cas_dir, ca_id)
 
     def create_ssh_ca(self, ca_id, ca_name):