Add feature generation support for multi-module projects

[TrevCraw]

• Track class files from all modules that are in the Maven Reactor build order or Gradle multi project build
  • Completed for Maven with (Track class files #1270)
• Include multi-module classes as input to the binary scanner when necessary (ie. Passing all classes, class files have been updated). (Completed with Track class files #1270)
• Generate the feature list XML file in the server configuration directory that has no other modules depending on it.
  • Completed for Maven with Handle multi module feature gen #1290

Note: multi module support is not available for Gradle yet, but this code may only be needed in ci.common, so it should work for both Maven and Gradle. If necessary, open a separate issue in ci.gradle.

[ericglau]

Completed for Maven. Opened separate issue OpenLiberty/ci.gradle#654 for Gradle.