Greatly reduce code duplication in rspec tests of db::mysql

Use shared examples to avoid duplicating tests for both platforms.

Change-Id: I16a77a284070e243c2a46675af419e635a139969
Improve openstacklib::db::mysql test coverage

* Add tests for openstacklib::db::mysql::host_access
* Add tests for other overridable parameters in db::mysql
* Do not test implementation details of host_access from
  within openstacklib::db::mysql tests.

Change-Id: Ifcf3820a575f932313a62b9d294ebd92a5055cf5
Fix support for puppetlabs-stdlib<4.2.0

Support for non-array value in the function concat() was added
in puppetlabs-stdlib 4.2.0.

This change adds a fix to support puppetlabs-stdlib<4.2.0
by converting $host to an array.

Change-Id: Ib8e4c7a5f788d1e0bd7440bc93b560df8e39fcf4
Merge "Greatly reduce code duplication in rspec tests of db::mysql"
Merge "Improve openstacklib::db::mysql test coverage"