Use HOME env var for db file

[sleshchenko]

For some reasons ~ does not work correctly in Vertx Devfile

This PR replaces it with ${HOME}

It's needed to eclipse-che/che-devfile-registry#18

[metlos]

Note that this can be worked around by specifying the jdbc url as an environment variable:

JDBC_URL=jdbc:h2:/tmp/db java -jar target/*fat.jar

This should work in any Spring Boot application where the configuration properties can be read from multiple sources by default..

[sleshchenko]

@metlos Thanks for sharing info about overriding Spring Boot Application configuration.
Closing this PR since for me it looks like it's even better to specify DB file path during application start instead of relying on the default value.