bug 2088: test suite refactoring to deal with t/override_context_prefs.pm

bug 2088: test suite refactoring to deal with t/override_context_prefs.pm

Some minor changes to get the test suite working a bit better:
I removed a superfluous method from t/lib/KohaTest.pm.
I made each barcode for the items added in KohaTest.pm unique so that they would actually get inserted.

Then, I removed t/override_context_prefs.pm. If you need that functionality, you're a database
dependent test and should be a module in t/lib.
So, I deleted all of the trivial .t tests that just 'use'd their modules and had no other
tests and replaced them with lib/KohaTest/*pm modules that do a little bit more checking
on those modules.
I removed the references to override_context_prefs.pm in all of the other .t modules.
They all pass now with no override_context_prefs.pm module.

The database_depenedent.pl test script still does not pass entirely. There's a problem with the zebra index
not being reset each time that the tables are truncated. I'll get to that.

no functional or documentation changes here.

Signed-off-by: Joshua Ferraro <jmf@liblime.com>