Prevent interruption of AcToolStartupHookServiceImpl

[kwin]

The underlying Felix SCR implementation waits at most 5 seconds (https://github.com/apache/felix-dev/blob/38543865717f8b9228243cafd75045c6ad2ea02e/scr/src/main/java/org/apache/felix/scr/impl/manager/ScrConfiguration.java#L60) until it interrupts activate methods of DS components. Also there is known race conditions (https://issues.apache.org/jira/browse/FELIX-5612), therefore we should probably
a) always run asynchronously and
b) find a way to defer shutting down AEM during the image build
for the ACToolStartupHookServiceImpl (https://github.com/Netcentric/accesscontroltool/blob/develop/accesscontroltool-startuphook-bundle/src/main/java/biz/netcentric/cq/tools/actool/startuphook/impl/AcToolStartupHookServiceImpl.java#L99) until a) is finished

[kwin]

#804 added the option to run installation asynchronously via Sling Jobs. Not sure to which degree Jobs are executed during image build, though.