amis: Fix CentOS base AMI dependencies
amis: Fix CentOS base AMI dependencies

The Chef recipes expect pip and awscli to be installed, so do so.
They also expect the base AMIs to have SELinux disabled, so disable
SELinux, since CentOS community AMIs apparently enable it by
default.

Signed-off-by: Brian Barrett <d66978685279cdc34963e2646fc378944676ad60@amazon.com>

rajachan/cfncluster-cookbook,rajachan/cfncluster-cookbook,rajachan/cfncluster-cookbook,rajachan/cfncluster-cookbook