Repair clear holds shelf transaction timeout

Initiate our cstore transaction after making the initial, potentially
long-running call to collect the clear-shelf holds to process.
Otherwise, the cstore transaction may time out while waiting on the
holds retrieval to complete.

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Ben Shum <bshum@biblio.org>