Disable forking for better Docker compatibility

[kiview]

In the light of #62 and #33, I'd like to contribute the proposed --no-forks flag. However, I would need a little bit of explanation to understand the original reasoning behind forking.

As a little bit of context, I'm a maintainer of https://github.com/testcontainers/testcontainers-java/ and I think stellar could be a very good edition to our database modules.

[B-Galati]

@kiview as this repository seems unmaintained. Did you find another solution?

[B-Galati]

Currently, I am basically doing docker run [...] stellar snapshot && sleep 6