man: Fix automake seddery

Because this is an automakefile, things inside @@ get expanded, which
means your sed ends up saying s|/var/log|/var/log| and your manual pages
still have @logdir@ in them. Fix this by hiding the @s inside a trivial
character range, which keeps the pattern preserved all the way into the
Makefile.

Signed-off-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>