This change ensures selinux is disable on CentOS7 beaker job to
workaround an selinux denial currently blocking the gate.
Backport note:
This commit includes the following two commits which fixed some issues
with the task to disable selinux.
e7d7ba5c8f
Fix ansible error when making selinux permissive
ba73591f22
Update selinux mode by root
Related-Bug: #1927210
Change-Id: Ie1bf3ebdb2642e24beb10d80878b8eecd67ce9e0
(cherry picked from commit 952ae0e3f1)
(cherry picked from commit 1d06ff2e11)