installation: usage of sanitised database name
installation: usage of sanitised database name

* Uses sanitised variable `$SAFE_NAME` (from `$VENAME`) in
  installation guide for the database name and user. (closes #3303)
  (closes #3304)

Co-authored-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>
Signed-off-by: Alexander Wagner <d3da4f3d1e1895133471112f50716122e1c26e75@desy.de>

inveniosoftware/invenio,inveniosoftware/invenio,tiborsimko/invenio,tiborsimko/invenio