Make sure SLO's bulk-delete logger is configured

The SLO middleware supports deletion of an object and all its
segments; internally, it uses the same code as the bulk middleware to
do this (swift.common.middleware.bulk.Bulk).

If something goes wrong in the bulk delete, the Bulk object logs the
exception; however, SLO's Bulk object's logger always has the default
logging config, so if you've got a non-default logging setup
(e.g. syslog to a remote log host), this one exception message goes
somewhere else (e.g. local syslog).

This patch makes SLO and its bulk deleter share a logger so all the
messages go to the same place.

Change-Id: Idb01b5640257a02dbb9c698851a14ad8fba11a2d
lower the default yield frequency for bulk requests

closes bug 1270246

DocImpact

Change-Id: If7f484d1a580e991896ac55f822655110266f3fa
Merge "Make sure SLO's bulk-delete logger is configured"
Merge "lower the default yield frequency for bulk requests"