Allow to reuse ewoks config file with EWOKS_CONFIG env var

Closes #26 (closed)

This field is optionnal.

It is usually setup with EWOKS_CONFIG="beacon:///ewoks/config.yml"

Here is what i did at the tomo simulator:

environment=
     TANGO_HOST="localhost:10000",
     BEACON_HOST="localhost:10001",
+    EWOKS_CONFIG="beacon:///ewoks/config.yml",
     ISPYB_DATABASE_URL="localhost:4406/test",
     ISPYB_DATABASE_USER="test",
     ISPYB_DATABASE_PASSWORD="test",
-    CELERY_BROKER_URL="redis://localhost:10002/2",
-    # CELERY_BROKER_URL="amqp://guest:guest@localhost/default",
-    # CELERY_BROKER_API_URL="http://guest:guest@localhost:15672/api/",
     CELERY_BROKER_QUEUE="default",
-    CELERY_BACKEND_URL="redis://localhost:10002/3",
     CELERY_EWOKS_TASK_QUEUES="tomo-sinogram-reconstruction",
     EWOKS_GRAPH_LOCATION="pyrsrc://tomovis.resources/graphs",
     MIMAS_SPECIFICATIONS="sidecar.celery.mimas.specifications"