Exploded loose app format doesn't include separate 'target/classes' entry; doesn't update app using mvn compile outside of all-in-one goals

[scottkurz]

The "exploded" loose app format added for #1104 in v3.5.2 was done a bit incorrectly, without a separate entry mapping "target/classes" to "WEB-INF/classes".

It's clear if you compare the generated loose app format to the one in the UFO design linked from #1104, however it's a bit of a subtle use case that's broken which might be forgotten somewhat if you think of loose apps mainly being run together with dev mode and/or the all-in-one goals in general (dev + run both). So let me elaborate on a recreate to show what has been missed:

Good case

1. git clone git@github.com:OpenLiberty/guide-getting-started.git; cd guide-getting-started/finish
2. upgrade liberty-maven-plugin to latest v3.6.1
3. mvn liberty:run (This provides a shortcut to getting everything installed and deployed)
4. Add a println in SystemResource#getProperties()
5. mvn compile (from a separate terminal... or use an IDE)
6. curl http://localhost:9080/dev/system/properties
7. In liberty:run window, or via cat target/liberty/wlp/usr/servers/defaultServer/logs/messages.log (and observe new println value in output)
8. Ctrl+C (back in liberty:run window)
9. cat target/liberty/wlp/usr/servers/defaultServer/apps/guide-getting-started.war.xml (observe "..../target/classes" entry in loose app XML mapping to /WEB-INF/classes, e.g:

<dir sourceOnDisk="C:\aaa\Work\tmp\aasdfadsf\guide-getting-started\finish\target\classes" targetInArchive="/WEB-INF/classes"/>

Bad case

1. Add this config to maven-war-plugin in pom.xml (forcing use of the newer "exploded" format)

                <configuration>
                    <filteringDeploymentDescriptors>true</filteringDeploymentDescriptors>
                </configuration>

2. mvn liberty:run (shortcut to redeploy)
3. Change the println value in SystemResource#getProperties()
4. mvn compile
5. curl http://localhost:9080/dev/system/properties
6. In liberty:run window, or via cat target/liberty/wlp/usr/servers/defaultServer/logs/messages.log (and observe OLD println value in output, NOT the NEW)
7. Ctrl+C
8. cat target/liberty/wlp/usr/servers/defaultServer/apps/guide-getting-started.war.xml (observe NO "target/classes" entry in loose app XML)

This should be an easy enough fix.