LP#1653742 Copy tree authoritative API share cstores

LP#1653742 Copy tree authoritative API share cstores

Avoid opening one cstore connection per requested org unit in the
open-ils.cat.asset.copy_tree.retrieve.authoritative API by creating a
single shared cstore connection at the top of the API shared by all
API actions.

To test:

1. In one terminal:

% tail osrfsys.log | grep transaction.begin

2. In another terminal:

srfsh% request open-ils.cat
open-ils.cat.asset.copy_tree.retrieve.authoritative "AUTOTOKEN", 217,
[1,2,3,4,5,6,7,8,9]

3. 9 cstore transactions are opened before patching.  After patching,
only 1 is created.

Signed-off-by: Bill Erickson <berickxx@gmail.com>