Add rax_meta module

Also update rax to mirror meta value normalization from rax_meta
Fix order of merging variables for the combined cache

Fixes #7598
Merge branch 'rax-meta' of https://github.com/sivel/ansible into sivel-rax-meta
Adding the new rax_meta module to the CHANGELOG
Merge branch 'sivel-rax-meta' into devel