for Oracle, Postgresql, Mysql
  create users:  xwiki, xwiki1, xwiki2

1. Install wiki as usial
  1.1 - wiki is created on empty database.
  1.2 - HelloWprld page is created. Wiki with hello-world is created.
2. set xwiki.db to xwiki1.  drop all tables in scheme xwiki.
  2.1 - xwiki1 is created on empty databsase
        HelloWorld-XWIKI1 page is created.
  2.2 - HelloWorld-XWIKI1 page is restired after startup/shutdown
3. set xwiki.db to xwiki2.  
  3.1 - xwiki2 is created on empty databsase
        HelloWorld-XWIKI2 page is created.
  3.2 - HelloWorld-XWIKI2 page is restored after startup/shutdown
4. set xwiki.db to xwiki1.  
  4.1 - HelloWorld-XWIKI1 page is restired after startup/shutdown
5. Setup virtual wiki (load XAR files)
  5.1.  switch to virtual mode. create virtual wiki without 
        xwiki.db and virtual.db.prefix. Check that wikie-s are different.
        check startup/shutdown.
  5.2.  virtual mode with xwiki.db and without xwiki.virtual.db.prefix.
  5.3.  virtual mode with xwiki.db="xwiki1" and with xwiki.virtual.db.prefix=q1
     note: before create in database schema "q1xwiki1"

Oracle:
 1.1 - OK
 1.2 - OK
 2.1 - OK
 2.2 - OK
 3.1 - OK
 3.2 - OK
 4.1 - OK
 5.1 - OK
 5.2 - OK
 5.3 - OK

Postgresql
 1.1 - OK
 1.2 - OK
 2.1 - OK
 2.2 - OK
 3.1 - OK
 3.2 - OK
 4.1 - OK

MySql
 1.1 - OK
 1.2 - OK
 2.1 - OK
 2.2 - OK
 3.1 - OK
 3.2 - OK
 4.1 - OK
 5.1 - OK  (if we say 'root' for username in hibernate.cfg) 
 5.2 - OK
 5.3 - OK