Enhancement: Docker image for cs3org/revad:VERSION-eos

Based on eos:c8_4.8.15 (Centos8, version 4.8.15). To be used when the
Reva daemon needs IPC with xrootd/eos via stdin/out.

https://github.com/cs3org/reva/pull/1386
https://github.com/cs3org/reva/pull/1389
