move server man pages to section 8

Change-Id: I8f8241241daa9cd4cca002dba4ead0f1f61a21a7
docs: add root notice to all server man pages

Change-Id: I8198fb3ecfcac0540b883944e4696f519517f988
docs: man page for beaker-repo-update

Change-Id: I1834a7a6179a7e5da1b1d8a1719f5614bd9fbf5a
docs: describe how to handle custom distros

Bug: 1132764
Change-Id: I37285ba58d7eb1790066042ac627d6ccea4f572f