Installer script doesn't work with PostgreSQL 9.6

09:10:44.826 [Main] INFO  org.opennms.core.schema.Migrator - validating database version
* using 'postgres' as the PostgreSQL user for OpenNMS
* using 'opennms' as the PostgreSQL database name for OpenNMS
09:10:44.922 [Main] INFO  org.opennms.core.schema.Migrator - validating database version
09:10:44.933 [Main] INFO  org.opennms.core.schema.Migrator - creating OpenNMS user, if necessary
java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.opennms.bootstrap.Bootstrap$4.run(Bootstrap.java:460)
	at java.lang.Thread.run(Thread.java:745)
Caused by: org.opennms.core.schema.MigrationException: an error occurred creating the OpenNMS user
	at org.opennms.core.schema.Migrator.createUser(Migrator.java:339)
	at org.opennms.core.schema.Migrator.prepareDatabase(Migrator.java:447)
	at org.opennms.install.Installer.install(Installer.java:254)
	at org.opennms.install.Installer.main(Installer.java:989)
	... 6 more
Caused by: org.postgresql.util.PSQLException: ERROR: unrecognized role option "createuser"
  Position: 54
	at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2284)
	at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:2003)
	at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:200)
	at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:424)
	at org.postgresql.jdbc.PgStatement.executeWithFlags(PgStatement.java:321)
	at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:313)
	at org.opennms.core.schema.Migrator.createUser(Migrator.java:337)
	... 9 more

Remove the long-deprecated CREATEUSER/NOCREATEUSER options from CREATE ROLE and allied commands (Tom Lane)

CREATEUSER actually meant SUPERUSER, for ancient backwards-compatibility reasons. This has been a constant source of confusion for people who (reasonably) expect it to mean CREATEROLE. It has been deprecated for ten years now, so fix the problem by removing it.