rsyslogd: fixed szarp-base package configuration on some systems

* rsyslog is not required by SZARP, so szarp-base package should be able
  to successfully finish 'configure' step without rsyslogd.

debian/szarp-base.postinst

@@ -11,17 +11,28 @@ case "$1" in
     configure)
 
     # apply appropriate discard action directive in rsyslogd configuration
-    RSYSLOG_TEM="/opt/szarp/resources/rsyslog_conf_TEMPLATE"
-    RSYSLOG_CFG="/etc/rsyslog.d/szarp.conf"
-    RSYSLOG_VER=$(/usr/sbin/rsyslogd -v | awk 'NR==1{print $2}' | awk -F'.' '{print $1}')
-
-    if [ -f "$RSYSLOG_TEM" ]; then
-        if [ "$RSYSLOG_VER" -gt 6 ]; then
-            sed 's/DISCARD_ACTION/stop/' "$RSYSLOG_TEM" > "$RSYSLOG_CFG"
+    if command -v "rsyslogd" >/dev/null 2>&1; then
+        echo "Installing rsyslogd configuration for SZARP..."
+
+        RSYSLOG_TEM="/opt/szarp/resources/rsyslog_conf_TEMPLATE"
+        RSYSLOG_CFG="/etc/rsyslog.d/szarp.conf"
+        RSYSLOG_VER=$(rsyslogd -v | awk 'NR==1{print $2}' | awk -F'.' '{print $1}')
+
+        if [ -f "$RSYSLOG_TEM" ] && [ -d "$(dirname "$RSYSLOG_CFG")" ]; then
+            if [ "$RSYSLOG_VER" -gt 6 ]; then
+                sed 's/DISCARD_ACTION/stop/' "$RSYSLOG_TEM" > "$RSYSLOG_CFG"
+            else
+                # tidle character is deprecated since version 7
+                sed 's/DISCARD_ACTION/~/' "$RSYSLOG_TEM" > "$RSYSLOG_CFG"
+            fi
+
+            echo "Configuration for rsyslogd successfully installed."
         else
-            # tidle character is deprecated since version 7
-            sed 's/DISCARD_ACTION/~/' "$RSYSLOG_TEM" > "$RSYSLOG_CFG"
+            echo "ERROR: failed to install rsyslogd configuration for SZARP. Abort."
+            exit 1
         fi
+    else
+        echo "WARNING: no rsyslogd found, SZARP-specific configuration will not be installed."
     fi
 
     /opt/szarp/bin/install_vim || true