Add a function which converts :undef values to nil values
to solve the compatibility problems with puppet4.
Apply this function to the bootstrap repository list.
Related-Bug: 1668995
Change-Id: Idfd793a1f8cc64361cb29d4b513e10c92da57151
Replace the merge_yaml_settings resource with the
merge_yaml module. This module introduced more advanced
version of the merge_yaml_settings resource with
additional options to control the merging behavior.
There are also resources with alternative implementation
of a configuration merging types and providers. They
are working in the same way as the "concat" module does
by assembling the resulting data structure from a set of
fragments. This should be much more puppet-master frinedly.
These types are not used anywhere yet but may be used later.
Related-Bug: 1614279
Change-Id: Ieaa8fc840f6a91a8d10e0670bd60d07692e2cb7d