debian: Fix log rotation.

Commit 24e81092a1 (debian: Bring Debian packaging in-line with new file
locations) introduced an ambiguous "--t" option invoking ovs-appctl, so
ovs-vswitchd and ovsdb-server were not reopening their log files following
log rotation.  This fixes the problem by correct the option name.

Reported-by: Paul Ingram <paul@nicira.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>