test: increase dgram timeout for armv6

test-dgram-broadcast-multi-process.js and
test-dgram-multicast-multi-process.js were failing on Pi 1 because the
test was timing out. Changed static 5000ms timeout to a dynamically
determined timeout based on the processor using
common.platformTimeout().

PR-URL: #2808
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>

Author: Trott

test/internet/test-dgram-broadcast-multi-process.js

@@ -7,7 +7,7 @@ var common = require('../common'),
     Buffer = require('buffer').Buffer,
     fork = require('child_process').fork,
     LOCAL_BROADCAST_HOST = '255.255.255.255',
-    TIMEOUT = 5000,
+    TIMEOUT = common.platformTimeout(5000),
     messages = [
       new Buffer('First message to send'),
       new Buffer('Second message to send'),

test/internet/test-dgram-multicast-multi-process.js

@@ -6,7 +6,7 @@ var common = require('../common'),
     Buffer = require('buffer').Buffer,
     fork = require('child_process').fork,
     LOCAL_BROADCAST_HOST = '224.0.0.114',
-    TIMEOUT = 5000,
+    TIMEOUT = common.platformTimeout(5000),
     messages = [
       new Buffer('First message to send'),
       new Buffer('Second message to send'),