Ganeti often gets installed with man pages but without design
documents. This makes sense, as design documents aim at Gaenti
developers, while man pages are also for persons just using
Ganeti. Therefore, this patch removes references to draft design
documents. For the other references,
- it adds a bit more explanation so that the man page is self-contained,
- reduces the reference to the name of the document, and
- adds the Ganeti version where it was implemented, so that it
  easier to find on docs.ganeti.org.

Fixes issue #921.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>