Bug 27071: Use GetReservesControlBranch to pick the branch

Bug 27071: Use GetReservesControlBranch to pick the branch

Pretty much like the opac-reserve.pl does, this patch makes the staff
request.pl script get the branch from the specialized routine from
C4::Reserves instead of falling back to userenv.

To test:
1. Follow the original test plan:
- Create two local hold groups containing distinct lists of libraries.
- In default rules for all libraries, set Hold Policy = "From local hold group" and Hold pickup library match to "Patron's hold group"
- Make sure AllowHoldPolicyOverride is set to Don't Allow

- Make sure you're logged in at a library in Group 1
- Find a bib with only 1 item from Group 1. Confirm you can place a hold on this title for a patron in Group 1 (correct), but not for a patron in Group 2 (correct).
- Find a bib with only 1 item from Group 2. Confirm you cannot place a hold for a patron from Group 1 (correct), BUT you also cannot place a hold for a patron from Group 2 (incorrect) -- Koha gives the erroneous message "pickupNotInHoldGroup"

- Change your library to a something in Group 2
- Find a bib with only 1 item from Group 1. Confirm you cannot place a hold on this title for a patron in Group 1 (incorrect), and not for a patron in Group 2 (correct).
- Find a bib with only 1 item from Group 2. Confirm you cannot place a hold for a patron from Group 1 (correct), but you can place a hold for a patron from Group 2 (correct)
=> FAIL: Things expected to fail on the plan, fail.
2. Apply this patches
3. Repeat 1
=> SUCCESS: It now works!

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>