*.install: Using more get_mirror to avoid hardcoding URLs

This is clearly better to use get_mirror instead of using hardcoded URLs
puppet-master.install: assume yes for puppetlabs-release package remove
openstack-controller: Update case, add centos support
doc: yum is a dependency to build RHEL like system
get_mirror: the lack of mirror is not fatal

There is no reason to fail if we can't provide a proper
mirror. The tools may use a default repository or another
media like a locak directory.
trivial refactoring: simplify kvm detection
enable strict mode
no need to do prior detect_kvm() exec