export_report: fix perl warnings

Use local file handles, use three argument open.
Don't modify arguments in perl grep (use sed instead)

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: WANG Cong <amwang@redhat.com>
Cc: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>