slaprunner: Fix bashism in Nginx & Supervisord logrotate entries
kill -SIGXXX works only in bash and not when the shell is e.g. dash, for example:
$ kill -SIGUSR1 1
/bin/sh: 2: kill: Illegal option -SThis way log rotation for slapproxy.log & friends was not properly working.
Fix it by using kill -XXX form which is supported everywhere.