[test_dhcp] Drop extra quotes

This test is failing for TF with
'test.domain' not in 'search bad\nnameserver 10.100.0.2\n'

Dropping extra quotes around domain name resolves issue.
Tested with OVS setup test is passing as well.

Related-PROD: PRODX-26370
Change-Id: I2583a1cf24ac19b60f8ef771ee9a4e5bf271ae3e
(cherry picked from commit 1d0a3c3bf0ea8a1f490006ebcaea8ec629a84061)
1 file changed