openurltracker table should be created through "CREATE IF NOT EXISTS"

[bram-atmire]

Context

The IRUS functionality to submit repository usage stats to the 3rd party IRUS collector, was previously added to DSpace through a 3rd party patch. As of DSpace 7, this functionality is part of DSpace out of the box. This feature relies on a DB table called "openurltracker"

https://wiki.lyrasis.org/display/DSDOC7x/Exchange+usage+statistics+with+IRUS

Describe the bug
The standard DB migration scripts will break for those institutions that previously already had the IRUS patch, and the openurltracker table in the database.

Instead of simply trying to CREATE the openurltracker table, the DSpace 7 migration should do this as CREATE IF NOT EXISTS

To Reproduce
Steps to reproduce the behavior:

1. Load a DSpace 5 or 6 DB that already had the openurltracker table
2. Try to execute the standard DSpace 7 DB migration

Expected behavior
The migration should not fail because of the openurltracker table already being present.