Fix intermittent failures in testevpncasesvxlan

[vimal]

Below DNS query fails randomly. Need to retry this query multiple times.

2
018-06-20 03:03:51,561 - INFO - Result for Dns Query is ; <<>> DiG 9.9.5-3-Ubuntu <<>> @13.1.1.253 www.google.com^M
; (1 server found)^M
;; global options: +cmd^M
;; Got answer:^M
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 60039^M
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1^M
^M
;; OPT PSEUDOSECTION:^M
; EDNS: version: 0, flags:; udp: 4096^M
;; QUESTION SECTION:^M
;www.google.com. IN A^M
^M
;; Query time: 1 msec^M
;; SERVER: 13.1.1.253#53(13.1.1.253)^M
;; WHEN: Tue Jun 19 21:33:50 UTC 2018^M
;; MSG SIZE rcvd: 43

2018-06-20 03:03:51,562 - ERROR - DNS Query for www.google.com Failed Not Expected
2

[OpenContrail Admin (ci-admin-f)]

Review in progress for https://review.opencontrail.org/43982
Submitter: vimal (<email address hidden>)