Support tomcat root

[csbarnet]

No description provided.

[buehner]

Hi. Thank you for the PR. Could you add a small section to the README to explain this new feature?

[csbarnet]

@reinout thank you for the comments and suggestions.

While my proposed change (with a couple of fixes) works ok for building a custom image, I'd like to try another approach that allows someone to change the context path after the image is built instead. I think that I can do this by either: turning off autodeploy and deployonstartup in server.xml and changing the context.xml or by moving the geoserver webapp files out of the /webapp path and altering the context.xml (according to tomcat 9 docs).

Is one of these approaches preferred? Also, should I close this pull request and start fresh, or just make those changes to this pull request branch?

[csbarnet]

This version keeps all of the geoserver files in /webapps/geoserver, but changes the context path by setting the docBase and path attributes in a context element in server.xml.

AFAIK, this is the only way to accomplish this without moving the docBase for the app context out of the host's appBase.

From the Tomcat docs:

If you want to deploy a WAR file or a directory using a context path that is not related to the base file name then one of the following options must be used to prevent double-deployment:

Disable autoDeploy and deployOnStartup and define all Contexts in server.xml
Locate the WAR and/or directory outside of the Host's appBase and use a context.xml file with a docBase attribute to define it.

Some relevant Tomcat 9 documentation is here:
naming
defining a context