make taler-exchange-offline a 'normal' user with shell

debian/etc-taler-exchange/taler/secrets/exchange-db.secret.conf

@@ -4,7 +4,7 @@
 
 # Typically, there should only be a single line here, of the form:
 
-CONFIG=postgres:///DATABASE
+# CONFIG=postgres:///DATABASE
 
 # The details of the URI depend on where the database lives and how
 # access control was configured.

debian/taler-exchange-offline.postinst

@@ -4,20 +4,18 @@ set -e
 
 . /usr/share/debconf/confmodule
 
-TALER_HOME="/var/lib/taler"
-
 case "${1}" in
 configure)
 
   if ! getent group taler-exchange-offline >/dev/null; then
-    addgroup --quiet --system taler-exchange-offline
+    addgroup --quiet taler-exchange-offline
   fi
 
   if ! getent passwd taler-exchange-offline >/dev/null; then
-    adduser --quiet --system \
+    adduser --quiet \
+      --disabled-password \
       --ingroup taler-exchange-offline \
-      --no-create-home \
-      --home ${TALER_HOME} taler-exchange-offline
+      taler-exchange-offline
   fi
 
   ;;