test: Fix rare race condition in TestZoneReload (#4617)
test: Fix rare race condition in TestZoneReload (#4617)

The following test failure for `TestZoneReload` can be observed
periodically:

`file_reload_test.go:58: Expected two RR in answer section got 2`

This failure can be consistently reproduced using the following command
(on my machine, at least):

`( cd test ; go test -v -race -run "TestZoneReload" ./... -count=500)`

test/file_reload_test.go:

Address a typo in a test failure message.

Sleep for double the file reload interval to avoid a rare
race condition between test code and the file plugin's reload code,
which is presumably a result of the time it takes to actually reload.

Signed-off-by: Stephen Greene <17ee0c5975fdf140e2b638af0c5bb5776a0f4822@redhat.com>
coredns/coredns,yongtang/coredns,chrisohaver/coredns