[docs] Updated logical architecture info

Referenced wiki.openstack.org/fuel architecture page,
instead of not well representative logical architecture
in PlantUML. Had to remove broken links to the blogposts
about using Facter to pass information to Puppet,
could not find those blogposts anywhere else in the Internet.
It appeared to be just two lines of text, which I combined
with existing architecture.rst, removing logical_arch.rst
completely.

Change-Id: Icba0d80e56d98391280c25355855122929819a92
Closes-Bug: #1313743
Merge "[docs] Updated logical architecture info"