Repair cstore transaction leak in A/T reactor helper

Repair cstore transaction leak in A/T reactor helper

This is not good:

my $copy = new_editor(xact=>1)->retrieve_asset_copy(...)

This opens a connection to a cstore drone and creates a
transaction without closing the transaction or connection, causing the
cstore drone to be idle and un-usable for the duration of the keepalive
timeout.

Signed-off-by: Bill Erickson <berick@esilibrary.com>