Remove trailing whitespace (#1955)

Prevent future; "remove trailing whitespace" PR, but adding a simple
presubmit that checks for this.

This presubmit flagged quite some offenders, remove all trailing
whitespace from. Apart from that there aren't any other changes.

Signed-off-by: Miek Gieben <miek@miek.nl>

test/hosts_file_test.go

@@ -17,7 +17,7 @@ func TestHostsInlineLookup(t *testing.T) {
                        hosts highly_unlikely_to_exist_hosts_file example.org {
                          10.0.0.1 example.org
                          fallthrough
-                      }	
+                      }
                     }`
 
 	i, udp, _, err := CoreDNSServerAndPorts(corefile)