dolphin: Implete TRUNCATE table (#697)

Author: kyleconroy

internal/endtoend/testdata/truncate/go/db.go renamed to internal/endtoend/testdata/truncate/mysql/go/db.go

@@ -3,6 +3,7 @@
   "packages": [
     {
       "path": "go",
+      "engine": "mysql:beta",
       "name": "querytest",
       "schema": "query.sql",
       "queries": "query.sql"

internal/endtoend/testdata/truncate/mysql/go/models.go

@@ -0,0 +1,4 @@
+CREATE TABLE bar (id serial not null);
+
+-- name: Truncate :exec
+TRUNCATE bar;

internal/endtoend/testdata/truncate/go/query.sql.go renamed to internal/endtoend/testdata/truncate/mysql/go/query.sql.go

@@ -0,0 +1,12 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "engine": "postgresql",
+      "name": "querytest",
+      "schema": "query.sql",
+      "queries": "query.sql"
+    }
+  ]
+}