Add support for SQL responses in key/value format (elastic#15845)

There are some queries like mysql `SHOW STATUS` that display the
results in a key/value format so they need to be scanned in a different
way, being the key the first column of the response and the value the
second one.

CHANGELOG.next.asciidoc

@@ -107,6 +107,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Add mesh metricset for Istio Metricbeat module {pull}15535[15535]
 - Add mixer metricset for Istio Metricbeat module {pull}15696[15696]
 - Make the `system/cpu` metricset collect normalized CPU metrics by default. {issue}15618[15618] {pull}15729[15729]
+- Add `key/value` mode for SQL module. {issue}15770[15770] {pull]15845[15845]
 - Add STAN dashboard {pull}15654[15654]
 - Add support for Unix socket in Memcached metricbeat module. {issue}13685[13685] {pull}15822[15822]
 

metricbeat/docs/modules/sql.asciidoc

@@ -30,7 +30,7 @@ metricbeat.modules:
 
   driver: "postgres"
   sql_query: "select now()"
-
+  sql_response_format: table
 ----
 
 [float]

x-pack/metricbeat/metricbeat.reference.yml

@@ -988,7 +988,7 @@ metricbeat.modules:
 
   driver: "postgres"
   sql_query: "select now()"
-
+  sql_response_format: table
 
 #--------------------------------- Stan Module ---------------------------------
 - module: stan

x-pack/metricbeat/module/sql/_meta/config.yml

@@ -6,4 +6,4 @@
 
   driver: "postgres"
   sql_query: "select now()"
-
+  sql_response_format: table

x-pack/metricbeat/module/sql/query/_meta/data_mysql_tables.json

@@ -0,0 +1,30 @@
+{
+    "@timestamp": "2017-10-12T08:05:34.853Z",
+    "event": {
+        "dataset": "sql.query",
+        "duration": 115000,
+        "module": "sql"
+    },
+    "metricset": {
+        "name": "query",
+        "period": 10000
+    },
+    "service": {
+        "address": "172.21.0.2:3306",
+        "type": "sql"
+    },
+    "sql": {
+        "driver": "mysql",
+        "metrics": {
+            "numeric": {
+                "table_rows": 1
+            },
+            "string": {
+                "engine": "MyISAM",
+                "table_name": "db",
+                "table_schema": "mysql"
+            }
+        },
+        "query": "select table_schema, table_name, engine, table_rows from information_schema.tables where table_rows \u003e 0;"
+    }
+}