plone_zope_conf_additional is not indented properly

[fulv]

If you specify a multi-line plone_zope_conf_additional value, it gets expanded in the buildout cfg without proper indentation. For example:

local-configure.yml:
...............................

plone_zope_conf_additional: |
    <product-config beaker>
        session.type        file
        session.data_dir  ${buildout:var-dir}/sessions/data
        session.lock_dir  ${buildout:var-dir}/sessions/lock
        session.key        beaker.session
        session.secret    somesecret
    </product-config>

The resulting buildout file looks like this:

[client1]
....
zope-conf-additional =
    <product-config beaker>
session.type        file
session.data_dir  ${buildout:var-dir}/sessions/data
session.lock_dir  ${buildout:var-dir}/sessions/lock
session.key        beaker.session
session.secret    somesecret
</product-config>

which causes this error:

An internal error occurred due to a bug in either zc.buildout or in a
recipe being used:
Traceback (most recent call last):
  File "/usr/local/plone-5.1/zeoserver/local/lib/python2.7/site-packages/zc/buildout/buildout.py", line 1994, in main
    user_defaults, command, args)
  File "/usr/local/plone-5.1/zeoserver/local/lib/python2.7/site-packages/zc/buildout/buildout.py", line 231, in __init__
    data['buildout'].copy(), override, set()))
  File "/usr/local/plone-5.1/zeoserver/local/lib/python2.7/site-packages/zc/buildout/buildout.py", line 1608, in _open
    fp, filename_for_logging, _default_globals)
  File "/usr/local/plone-5.1/zeoserver/local/lib/python2.7/site-packages/zc/buildout/configparser.py", line 234, in parse
    raise e
ParsingError: File contains parsing errors: /usr/local/plone-5.1/zeoserver/live.cfg
        [line 180]: 'session.type            file\n'
        [line 181]: 'session.data_dir        ${buildout:var-dir}/sessions/data\n'
        [line 182]: 'session.lock_dir        ${buildout:var-dir}/sessions/lock\n'
        [line 183]: 'session.key             beaker.session\n'
        [line 184]: 'session.secret          somesecret\n'
        [line 185]: '</product-config>\n'
        [line 197]: 'session.type            file\n'
        [line 198]: 'session.data_dir        ${buildout:var-dir}/sessions/data\n'
        [line 199]: 'session.lock_dir        ${buildout:var-dir}/sessions/lock\n'
        [line 200]: 'session.key             beaker.session\n'
        [line 201]: 'session.secret          somesecret\n'
        [line 202]: '</product-config>\n'

[fulv]

related: https://stackoverflow.com/questions/34004171/printing-a-variable-value-indented-in-a-yaml-file-using-ansible