stack/erp5: fix slowquery digest monitor promise

instance-mariadb.cfg.in:
  rename slowquerydex folder to slowquery_digest
mysql-querydigest.sh.in:
  exit 1 on error
  add date to the output file name of pt-query-digest to fit promise behavior
    https://lab.nexedi.com/nexedi/slapos.toolbox/blob/beb86eab2dee7178aa6e4795da0f56bb6cacaea1/slapos/promise/check_slow_queries_digest_result/__init__.py#L29
  review sh arguments handling
  end message: "ok" -> "Report generated successfully." or ..."failed with code $?"

stack/erp5/instance-mariadb.cfg.in

@@ -252,7 +252,7 @@ mariadb-ssl = ${:etc}/mariadb-ssl
 var = ${buildout:directory}/var
 log = ${:var}/log
 run = ${:var}/run
-slowquery =  ${monitor-directory:private}/slowquerydex
+slowquery = ${monitor-directory:private}/slowquery_digest
 
 [{{ section('resiliency-exclude-file') }}]
 # Generate rdiff exclude file in case of resiliency

stack/erp5/mysql-querydigest.sh.in

@@ -7,19 +7,20 @@ PT_QUERY_EXEC='{{pt_query_exec}}'
 
 if [ ! -d "$OUTPUT_FOLDER" ]; then
   echo "ERROR: output_folder don't exists"
-  exit 0
+  exit 1
 fi
 
-OUTPUT_FILE=${OUTPUT_FOLDER}/slowquery_digest.txt
-
-TODAY=`date +%Y%m%d`
+dashed_today=$(date +%Y-%m-%d)
+today=$(date -d "$dashed_today" +%Y%m%d)
 
-SLOW_LOG=$SLOW_QUERY_PATH-$TODAY
+SLOW_LOG="$SLOW_QUERY_PATH-$today"
+OUTPUT_FILE="$OUTPUT_FOLDER/slowquery_digest.txt-$dashed_today"
 
 if [ ! -f "$SLOW_LOG" ]; then
   echo "ERROR: cannot read mysql slow query log file $SLOW_LOG. Exiting."
   exit 1
 fi
 
-$PT_QUERY_EXEC $SLOW_LOG >  $OUTPUT_FILE
-echo "ok"
+"$PT_QUERY_EXEC" "$SLOW_LOG" > "$OUTPUT_FILE" && \
+echo "Report generated successfully." || \
+echo "Report failed with code $?"