Fixes "key ipv4_set slap-configuration:ipv4" referencing a non-existing
section (woops, copy/paste...).

Also, update documentation to state that web-checker can be disabled
altogether and that frontend-url is optional (it has a working default
value).
Also, provide replacements in frontend-url for easier configuration.
Also, stop depending on slap-network-information magical section.

Develop is bad anyway, but at least this fixes varnish software release in
master branch.

This automatically handle lxml installation.

Request the service with the software type pullrdiffbackup.

Real backup are added by request a slave with required parameters:
  hostname="example.org" (just to make think readable for human)
  connection="user@0.0.0.0" (ssh connection string)
  include="/src /home" (space separated directory path to backup)
  frequency="0 0 * * *" (crontab like periodicity string)

Optional parameters are:
  exclude="/home/userA /home/userB" (space separated directory path to not backup)
  sudo="True" (if the server to backup contains a local backupagent_rdiff-backup script which is callable with sudo)

Add a new section ["component"-output] to test the creation of the expected
build output.
The verification is simply done with the "test" command.

The output file are reference as section variable, which allow to reuse the
location in the software profile, and so, prevent harcoding the local directory
path in the software profile.

"-" elect as option caracter
Do not add slave reference by default in Connection Dict for publish

Loosened checks are considered safe enough, and the speedup on many-GB
FileStorage files is significant.

Split line more naturally (don't separate switch from related argument).
Use long options instead of abbreviations.

Also, reduce code duplication.