util: open mrafs-style logs with O_APPEND too

util: open mrafs-style logs with O_APPEND too

Commit b71a041364d28d6a56905a770cd20d1497ee26ec added the O_APPEND flag when
opening the log file to allow sites to use logrotate's "copy and truncate"
feature.

Add the O_APPEND to MR-AFS style logs as well so MR-AFS style logs can also be
handled correctly with logrotate, we have consistent open flags, and can remove
a duplicate call to open the log file descriptor.

Change-Id: I8370838e1e2c7ddaa042508d6b9cbe1299339f68
Reviewed-on: https://gerrit.openafs.org/12218
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>