slaprunner: Only cat if the file exit

  If there is no error, the raise can be missleading.

software/slaprunner/buildout.hash.cfg

@@ -27,7 +27,7 @@ md5sum = feee1dc29d160e0d796dab0ba767745f
 
 [instance-runner-import]
 filename = instance-runner-import.cfg.in
-md5sum = 0701cf6282efa28086990f73ec2a319f
+md5sum = 154be5ff86a145fca4c1358c15196efa
 
 [template-runner-export-script]
 filename = template/runner-export.sh.jinja2

software/slaprunner/instance-runner-import.cfg.in

@@ -118,7 +118,9 @@ input = inline: #!/bin/sh
        echo "Consistency check is too old.";
        exit 1;
     else
-      cat $${importer:restore-error-message-file}
+      if [ -f "$${importer:restore-error-message-file}" ]; then
+        cat $${importer:restore-error-message-file}
+      fi
       echo "More information can be found here : $RESILIENT_LOG_URL";
       exit $(cat $EXIT_CODE_FILE);
     fi