Bug 17539: Fix Already in a transaction error

Bug 17539: Fix Already in a transaction error

perl t/db_dependent/Reserves.t

1..72
ok 1 - use C4::Reserves;
ok 2 - CheckReserves Test 1
...
ok 52 - Reserve in waiting status cant be canceled
ok 53 - Reserving an ageRestricted Biblio without a borrower dateofbirth succeeds
DBD::mysql::db begin_work failed: Already in a transaction at
/usr/share/perl5/DBIx/Class/Storage/DBI.pm line 1489.
DBD::mysql::db begin_work failed: Already in a transaction at
/usr/share/perl5/DBIx/Class/Storage/DBI.pm line 1489.
at /usr/share/perl5/DBIx/Class/Schema.pm line 1080.
...
Koha::Object::store('Koha::Patron=HASH(0x9e43b20)') called at
/home/ubuntu/kohaclone/C4/Members.pm line 542
C4::Members::ModMember('borrowernumber', 658535, 'dateofbirth', '2001-11-02')
called at t/db_dependent/Reserves.t line 516

This patch fixes this issue by replacing dbh autocommit=0 with
txn_begin.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>