Can't enable second feature on originating site

Problem/Motivation

After first exporting a single feature and successfully enabling it on the originating site, when attempting to enable a second feature on the originating site, the feature does not enable and an error message like the following is displayed:

Unable to install [feature name], [list of configuration in the feature] already exist in active configuration.

Proposed resolution

Fix array merging error in FeaturesManager::listExistingConfig().

Remaining tasks

User interface changes

API changes

Data model changes