environment variables containing dots are not returned by System.getenv() in EnvironmentVariables

[lrozek]

I am running web application in following docker image tomcat:9.0.41-jdk8-openjdk-buster. I tried to override excludecategories via environment variable called p6spy.config.excludecategories. However in this image System.getenv() doesn't return environment variables that contain dot in a name. Therefore it is not possible to override any property via environment variables, because EnvironmentVariables doesn't see them.
Please refer for releated issue at docker-library/openjdk#135

Would it be possible to introduce support for environment variables with underscore notation, ie:
p6spy_config_excludecategories instead of p6spy.config.excludecategories

[typekpb]

@lrozek I think your idea is valid, feel free to provide PR for the desired solution