Log4j respects the configured "log4j2.is.webapp" property

When running an application with an embedded servlet container, the configuration should be able to enable shutdown hook registration, and avoid the "Log4j appears to be running in a Servlet environment, but there's no log4j-web module" warning.

Steps to reproduce:
1. configure log4j2.is.webapp = false
2. Start application with a dependency on the servlet-api
3. "Log4j appears to be running in a Servlet environment, but there's no log4j-web module available." warning is logged