Add openstack resource puller

Add puller in BackupManager, DB and Object to keep only one node to pull
volume-server attachment information from OpenStack.
To have multiple puller is okay, but with this, we can reduce unnecessary API
calls to OpenStack.
diff --git a/requirements.txt b/requirements.txt
index 1b57644..bc61474 100755
--- a/requirements.txt
+++ b/requirements.txt
@@ -11,8 +11,9 @@
 oslo.config>=8.1.0
 oslo.log>=4.4.0 # Apache-2.0
 oslo_versionedobjects
+oslo.utils>=3.40.0 # Apache-2.0
 openstacksdk>0.28.0
 pymysql
 parse
 # email
-# smtplib
\ No newline at end of file
+# smtplib