new type __yum_repo to manage yum repositories

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>
++changes

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>
rename parameter repo_uri to uri as requested by nico
rename parameter service_uri to uri as requested
Merge branch 'bugfix_issue_327' of https://github.com/dheule/cdist
CentOS support for __hostname

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>
++releasedate

Signed-off-by: Nico Schottelius <nico@bento.schottelius.org>
support for centos

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>
add centos support to __postfix* types

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>
ensure file exists

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>