use HTTP instead of HTTPS for epel repos

Sometime deployment fails with this error:

failed: [ec2-13-229-161-164.ap-southeast-1.compute.amazonaws.com] (item=[u'python', u'unzip', u'bash-completion', u'tmux', u'bind-utils', u'wget', u'git', u'vim-enhanced', u'at', u'ansible']) => {"changed": fals
e, "item": ["python", "unzip", "bash-completion", "tmux", "bind-utils", "wget", "git", "vim-enhanced", "at", "ansible"], "msg": "Failure talking to yum: File /var/cache/yum/x86_64/7Server/epel/metalink.xml does
not exist"}

When you google that error, you find a lot of issues related to EPEL and ssl (ca-certificates).