cordova-android v7.0.0 was released on Nov. 30th. Version 7 introduces some major changes and is not yet supported for Ionic Pro package builds.
Attempting to package using cordova-android 7.x.x will result in a failed build. The only significant error present in the logs is "ERROR: Job failed: exit status 1". Reverting to android-cordova v6.4.0 will resolve the issue.
Cordova v8 was released on Dec. 14th, 2017. It defaults to cordova-android v7 when the android platform is added. Users who have updated to Cordova v8 will need to update their package.json and config.xml files as shown below.
<engine name="android" spec="6.4.0" />