[monitor] promise-check-slapgrid: prevent display sensitive information in promise output

This promise fail if slapgrid failed to process the partition and verbose the failed buildout log. It's possible that buildout logs contain information that should not be public, so put the log in a private folder and add the link to it to the promise result.

stack/monitor/buildout.hash.cfg

@@ -15,4 +15,4 @@
 # not need these here).
 [monitor2-template]
 filename = instance-monitor.cfg.jinja2.in
-md5sum = 5027f0b1abcc28ce3817cd70fb667a3b
+md5sum = 8ec30221c7560cab83ab879f9e9ff1f5

stack/monitor/instance-monitor.cfg.jinja2.in

@@ -369,8 +369,12 @@ mode = 700
 recipe = collective.recipe.template
 error-log-file = ${buildout:directory}/.slapgrid-${slap-connection:partition-id}-error.log
 input = inline:#!/bin/sh
+  BUILDOUT_LOG="${directory:log}/slapgrid-${slap-connection:partition-id}-error.log"
+  rm -f $BUILDOUT_LOG
   if [ -f "${:error-log-file}" ]; then
-    >&2 cat ${:error-log-file}
+    ln -sf ${:error-log-file} $BUILDOUT_LOG
+    >&2 echo "Buildout failed to process partition ${slap-connection:partition-id}"
+    >&2 echo "More info can be found here: ${monitor-base:base-url}/log/slapgrid-${slap-connection:partition-id}-error.log"
     exit 1
   fi
 output = ${monitor-directory:promises}/buildout-${slap-connection:partition-id}-status