Replace moved networking-guide with current location.
Replace non-existing anchor in https://galeracluster.com with page link.
Replace some more moved pages with new location.
Fix many places to use https instead of http.
Use internal RST link that can be verified instead of external one
for /user/security/index.html.
Checked with:
sphinx-build -a -E -W -d doc/build/doctrees -b linkcheck doc/source doc/build/html
Change-Id: I0368e509ba6702e0da1a9c96f7cee76a6d35b3e0
96c6635a15