Using K8s lease for lock

Using sherlock lib instead of tooz to support
Kubernetes lease.
diff --git a/requirements.txt b/requirements.txt
index 8a52b2b..32d5e37 100755
--- a/requirements.txt
+++ b/requirements.txt
@@ -18,5 +18,6 @@
 pymysql
 parse
 tooz # Apache-2.0
+sherlock>=0.4.1 # MIT
 # email
 # smtplib