Changes

db: flush after changing schema version

Flush the cache after changing the version, to make the scenario less
likely that after an unclean shutdown the DB gets restored with the
right table layout but wrong version.

When that happens, osmo-hlr tries to upgrade the database layout again
and fails with errors like "duplicate column name".

Related: SYS#7394
Change-Id: I5943a1cb3447c038c6e7972f68f9656b73a9248b