Added retries for NTP peers state test

Added retries for NTP peers state test because when the cloud
was deployed recently or NTP service was restarted with new
pools/servers, it takes some time to get expected NTP peers state.

Change-Id: Ibc4620e5fcc2d112361667992aa75fa68771aa0f
Realated: PROD-30970
diff --git a/test_set/cvp-sanity/requirements.txt b/test_set/cvp-sanity/requirements.txt
index b45a29e..fc42a2b 100644
--- a/test_set/cvp-sanity/requirements.txt
+++ b/test_set/cvp-sanity/requirements.txt
@@ -1,4 +1,5 @@
 pytest==3.7.1
+pytest-rerunfailures==7.0
 requests>=2.20.0
 flake8
 PyYAML