container: lib_finance: call root with $ROOTSYS

Non-packaged pre-compiled ROOT.cern is not installed to /usr/bin

container/src/finance/lib/lib_finance.bash

@@ -206,9 +206,11 @@ function lib_finance::reports()
 
 function lib_finance::root()
 {
+  [ -z "$ROOTSYS" ] && lib_utils::die_fatal
+
   # NOTE: will automatically load rootlogon.C
   pushd "${DOCKER_FINANCE_CONTAINER_REPO}/src/root/macro" 1>/dev/null \
-    && /usr/bin/root -l
+    && "${ROOTSYS}"/bin/root -l
   lib_utils::catch $?
 }