Oracle Docker container does not build

[snafu123]

/HDTN/containers/docker/oracle_linux/Dockerfile will not build sysvinit not available from Oracle 7. I suggest changing sysvinit-tools to systemd.

Also, instead of -j8 in the make step, perhaps make -j `nproc` is more generic

[rdudukov]

Thank you. We will try to clarify the instructions in the next revision!