Special handle host unreachable for window [issue #45]

--Overview
1. Catch keyword ```round trip time``` instead of catching ```(0%```
since ```round trip time``` will be dump to stdout if host is accessible
2. Remove default arguments ```addr``` from window implementation since
```addr``` has been appended twice
Fix bug on window platform

--Overview
1. Window's ping command treat '-i 2' as an invalid option. Therefore,
we must split them up. IE using ['-i', '2'] instead of ['-i 2']
Merge pull request #18 from mondwan/fix_window_unreachable

Fix window unreachable