Allow setting an entry point to an explicit pathed binary

[jrivard]

Description of the issue:
I'm trying to use an image where the entry point is not the java binary, and the java binary is in a different path than the default distroless image. (Specifically, adoptopenjdk/openjdk10)

Expected behavior:
I should be able to specify the image's java execution path

[coollog]

Hi @jrivard , thanks for suggesting this feature. We are considering allowing a custom entrypoint to be defined in #579.

[coollog]

@jrivard We have added support for defining a custom entrypoint via <container><entrypoint>. It is available in version 0.9.10.