L2SS-124 Fix the bug in lofar20rc.sh

The script can now locate itself and set LOFAR20_DIR accordingly.
This allows for multiple installations in parallel.

bootstrap/etc/lofar20rc.sh

+#! /usr/bin/env bash -e
 # Set up the LOFAR2.0 environment.
 # For the time being it is assumend that the LOFAR2.0 environment has to
 # co-exist with a LOFAR1 environment.
@@ -6,9 +7,10 @@
 # And export those directories for LOFAR in Tango Docker images.
 
 # Pass a directory as first parameter to this script.  This will
-# then be used as LOFAR20_DIR.  Otherwise the current directory will
-# be used.
-export LOFAR20_DIR=${1:-${PWD}}
+# then be used as LOFAR20_DIR.  Otherwise this file's directory
+# be used to determine the tango directory location.
+ABSOLUTE_PATH=$(realpath $(dirname ${BASH_SOURCE}))
+export LOFAR20_DIR=${1:-$(realpath ${ABSOLUTE_PATH}/../..)}
 
 # This needs to be modified for a development environment.
 # Example:  ~/lofar2.0/tango