Bug 19483: Fix test plan in t/db_dependent/www/*

Bug 19483: Fix test plan in t/db_dependent/www/*

t/db_dependent/www/* crashes test harness due to misconfigured test plan

prove t/db_dependent/www/

without defining KOHA_INTRANET_URL
bails out and marks the whole test suite as failed.
Test suite should not be failed if this optional WWW::Mechanize test
suite is not activated.

After this patch, the tests are properly skipped without failing the
whole tests.

This is important when running all tests under t, as this needlessly
fails the test suite.

Also handling of 'skip_all' is inconsistent in t/db_dependent/www
-tests, so this normalizes it to skip_all instead of bail_out

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>