Add Heka log decoder for MariaDB

In the future the Heka Lua sandboxes will be moved out of Kolla, and
installed in the Heka container using a deb or rpm package.

Partially implements: blueprint heka
Change-Id: Iad1e5177d239410a88546fc4ed8c23b9e46beef3

docker/heka/plugins/decoders/os_mysql_log.lua

+-- Copyright 2015-2016 Mirantis, Inc.
+--
+-- Licensed under the Apache License, Version 2.0 (the "License");
+-- you may not use this file except in compliance with the License.
+-- You may obtain a copy of the License at
+--
+--     http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+require "string"
+local l      = require 'lpeg'
+l.locale(l)
+
+local patt   = require 'os_patterns'
+local utils  = require 'os_utils'
+
+local msg = {
+    Timestamp   = nil,
+    Type        = 'log',
+    Hostname    = nil,
+    Payload     = nil,
+    Pid         = nil,
+    Fields      = {},
+    Severity    = nil,
+}
+
+local sp    = patt.sp
+local colon = patt.colon
+
+-- mysqld logs are cranky,the date is YYMMMDD, the hours have no leading zero and the "real" severity level is enclosed by square brackets...
+local mysql_grammar = l.Ct(l.digit^-6 * sp^1 *  l.digit^-2 * colon * l.digit^-2 * colon * l.digit^-2 * sp^1 * l.P"[" * l.Cg(l.R("az", "AZ")^0 / string.upper, "SeverityLabel") * l.P"]" * sp^1 * l.Cg(patt.Message, "Message"))
+
+
+function process_message ()
+    local log = read_message("Payload")
+    local logger = read_message("Logger")
+
+    local m = mysql_grammar:match(log)
+    if not m then return -1 end
+
+    msg.Logger = logger
+    msg.Payload = m.Message
+    msg.Fields.severity_label = m.SeverityLabel
+
+    return utils.safe_inject_message(msg)
+end