Virtual mode fails on Oracle with "ORA-01435: user does not exist"

XWIKI-5976 introduced escaping of the schema name for all DBs.

However this is causing an issue on Oracle (that we're just noticing now):

• Oracle converts user names in uppercase when no quotes is used. For example: "create user xwiki identified by xwiki;" creates a user named XWIKI (uppercase)
• In Hibernate.cfg.xml we just specify: <property name="connection.username">xwiki</property> and Hibernate seems to be passing this username as is to Oracle which converts it to uppercase. I couldn't find a way to tell Hibernate to escape the passed user, see https://hibernate.onjira.com/browse/HHH-6888

Since we escape the user in XWikiHibernateBaseStore.escapeSchema() Oracle fails with "ORA-01435: user does not exist"