Disallow unquoted LIKE '%suffix' placeholders in wbsearchentities

This wasn't a security issue since all other characters were quoted
properly. But it was a potential performance issue since LIKE
queries that start with a placeholder do not use any index.

It was simply a mistake that LIKE placeholders could be used (yes,
it worked in the API as well as in the UI). The software
architecture and how it is build and documented clearly does not
allow this.

I added two test cases:
1. Test if the prefixSearch option sucessfully returns something.
2. Test if '%' prefixed searches fail as they should.

Change-Id: I789dfd1c4b1ed770a0f6dde03225289d41da0089
Merge "Disallow unquoted LIKE '%suffix' placeholders in wbsearchentities"