PAM changes for supporting duo 2FA solution

Multi-Factor Authentication (MFA) for sshd+PAM
https://duo.com/product/multi-factor-authentication-mfa

Related-Prod: PROD-24422
Change-Id: Iddec5a5e99e7db5d7f173ad939d3fd0cac1cd22b
diff --git a/.travis.yml b/.travis.yml
index 875835a..dce83af 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -32,6 +32,7 @@
   - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2017.7 SUITE=system
   - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2018.3 SUITE=network
   - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2018.3 SUITE=system
+  - PLATFORM=epcim/salt:saltstack-ubuntu-xenial-salt-2018.3 SUITE=duo
   # - PLATFORM=epcim/salt:saltstack-ubuntu-bionic-salt-2017.7 SUITE=network
   # - PLATFORM=epcim/salt:saltstack-ubuntu-bionic-salt-2017.7 SUITE=system
   # - PLATFORM=epcim/salt:saltstack-ubuntu-bionic-salt-2018.3 SUITE=network