feat(cron): Make database-mysql.sql idempotent (spinnaker#614)

This makes the script idempotent, ideally to be run upon echo instance start to populate schema without having to check if the schema and users are already created.

Author: jmrodriguez-clv

Diff for: echo-scheduler/src/main/resources/db/database-mysql.sql

@@ -1,8 +1,8 @@
 SET tx_isolation = 'READ-COMMITTED';
 
-CREATE SCHEMA `echo` DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
-CREATE USER echo_migrate;
-CREATE USER echo_service;
+CREATE SCHEMA IF NOT EXISTS `echo` DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
+CREATE USER IF NOT EXISTS echo_migrate;
+CREATE USER IF NOT EXISTS echo_service;
 
 GRANT SELECT, INSERT, UPDATE, DELETE, EXECUTE, SHOW VIEW ON `echo`.* TO 'echo_service'@'%';
 GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, REFERENCES, INDEX, ALTER, LOCK TABLES, EXECUTE, SHOW VIEW ON `echo`.* TO 'echo_migrate'@'%';