Add level.exists property to all properties files

[MexicanHacker]

At this moment there is a property like this in the mysql.properties file:

level.exists=SELECT patch_level FROM patches WHERE system_name=? and patch_level=? \ and patch_in_progress <> 'F'

We should add the same property to the following files:

hsqldb.properties oracle.properties postgres.properties sqlserver.properties sybase.properties

[ulisespulido]

property was added to all files listed, closing this issue.