Allow to run AC Tool in phase "INSTALLED" rather than "PREPARE"

[kwin]

Currently the install hook for applying the yaml files is being executed in Phase "Prepare" (https://jackrabbit.apache.org/filevault/apidocs/org/apache/jackrabbit/vault/packaging/InstallContext.Phase.html). The reason for that is most probably due to the description in https://jackrabbit.apache.org/filevault/apidocs/org/apache/jackrabbit/vault/packaging/InstallHook.html which states that only from Phase "Prepare" you can throw exceptions which lead to package installation failures.

The drawback of using PREPARE though is that

1. you cannot create/update some initial content through a regular package structure and afterwards set ACLs for those in the same package.
2. You cannot use repository structures as workaround for missing support for global variables (Allow to reuse variables from other YAML files #257)
3. Initial content should be defined as regular content to be able to depend on it for application package type (https://issues.apache.org/jira/browse/JCRVLT-170). Those package types are not allowed to contain uncovered roots!

We should check again if PREPARE is really the only phase where Exception are being properly propagated.

[kwin]

Even in the most recent version only PREPARE exceptions are properly propagated (https://github.com/apache/jackrabbit-filevault/blob/a64860257de2450f804b0cdf55a5afc8686b2636/vault-core/src/main/java/org/apache/jackrabbit/vault/packaging/impl/InstallHookProcessorImpl.java#L150). I opened https://issues.apache.org/jira/browse/JCRVLT-289 for this.

[kwin]

https://issues.apache.org/jira/browse/JCRVLT-289 is fixed now and should be contained in the upcoming version 3.2 of Jackrabbit FileVault.

[kwin]

FileVault 3.2 is contained in AEM 6.4.2 or greater.

[kwin]

To still support older AEM versions, the default behaviour should stay as is, but optionally the hook should be executed in a different phase.