Fix for broken unified installers 4.3.4 throughout 4.3.15 with --static-lxml enabled

[tdkuehnel]

I have just checked out the following versions from

https://launchpad.net/plone/+milestone/4.3.2
https://launchpad.net/plone/+milestone/4.3.4
https://launchpad.net/plone/+milestone/4.3.9
https://launchpad.net/plone/+milestone/4.3.10
https://launchpad.net/plone/+milestone/4.3.11
https://launchpad.net/plone/+milestone/4.3.12
https://launchpad.net/plone/+milestone/4.3.14
https://launchpad.net/plone/+milestone/4.3.15

With every unified installer since the 4.3.2 (which is the last one that works out of the box) every version up to the latest (i assume stable) 4.3.15 the install fails when enabling --static-lxml with the following error:

...
Building lxml with static libxml2/libxslt; this requires Internet access,
and takes a while...

lxml build failed.
See log file for details.

install.log

...
Develop: '/usr/local/Plone4.3.4/zeocluster/src/z3c.recipe.staticlxml'
Couldn't find index page for 'zc.recipe.cmmi' (maybe misspelled?)
Getting distribution for 'zc.recipe.cmmi==1.3.5'.
While:
  Installing.
  Getting section lxml.
  Initializing section lxml.
  Installing recipe z3c.recipe.staticlxml.
  Getting distribution for 'zc.recipe.cmmi==1.3.5'.
Error: Couldn't find a distribution for 'zc.recipe.cmmi==1.3.5'.

This can be solved (thx 1letter Jan for the solution on https://community.plone.org/t/plone-4-3-15-unifiedinstaller-error-in-building-libxml2-libxslt-system-libraries/5674) by adding

index = https://pypi.python.org/simple

to the buildout section of the lxml_static.cfg in the base_skeleton dir of the unified installer.

As the error messages are only helpful when someone knows the interna of all the involved tools, i suggest at least to fix the latest stable of the 4.3 tree.