Bug 12748 - Fixes duplicate serials with an "expected" status bug

Bug 12748 - Fixes duplicate serials with an "expected" status bug

Added a new sub to Serials.pm to be able to get serials with their statuses.
Now the sub ModSerialStatus checks for other serials with an "expected" status before doing anything.

Also modified Serials.t to be able to test those changes.

Test Plan
1) Apply patch
2) Run ./t/db_dependent/Serials.t
3) Validate that there are no errors
4) Go on "Serial collection information" page for a serial of your choice
5) Click on "Generate next"
6) Change the status of the original serial from "late" to "expected"
7) Change the newly generated serial from "expected" to "delete"
8) Validate that there are no new serials created by instruction 7 and that the serial was deleted
9) Run ./t/db_dependent/Serials.t

With QA Fixes

- Use the constant instead of the code (1 vs EXPECTED)
- Avoid interpolation in query
- use selectall_arrayref instead of fetchall_arrayref

Signed-off-by: Liz Rea <liz@catalyst.net.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>