Added set_dns_nameserver script to contrail-utils package

This commit also changes the script rights

Change-Id: Iabed6d0ea37ffa5a5b2a89916ae7281cd9438d33
(cherry picked from commit 29d8443bd73eead994f6c4d42e55dff7e955bc87)
Merge "Added set_dns_nameserver script to contrail-utils package" into R1.10