Bug 1953 [1/3]: test suite improvements

Bug 1953 [1/3]: test suite improvements

Here are a few improvments to the test suite to make it easier to write some tests
for C4::Items

I extracted "tomorrow" and "yesterday" methods from a test module into the base class
so that they could be used by multiple test modules

Adding callnumber to items added in the test suite.

I recatored KohaTest::add_biblios a bit to remove the manual count of the number of
MARC::Fields that were added.

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