Support detecting mountpoints correctly (#7288)

Currently windows support was relying on Symlink as
a way to detect a drive, this doesn't work in latest
Windows 2016, fix this to use a proper mechanism by
using win32 APIs.

Additionally also add support for detecting bind mounts
on Linux.

vendor/vendor.json

@@ -1178,6 +1178,12 @@
 			"revision": "1e2299c37cc91a509f1b12369872d27be0ce98a6",
 			"revisionTime": "2017-11-09T13:50:42Z"
 		},
+		{
+			"checksumSHA1": "Hu8GoQK1euwtE4UjrhXepmk2NM8=",
+			"path": "golang.org/x/sys/windows",
+			"revision": "cd391775e71e684db52b63df9affd58269495083",
+			"revisionTime": "2019-02-22T15:12:32Z"
+		},
 		{
 			"checksumSHA1": "faFDXp++cLjLBlvsr+izZ+go1WU=",
 			"path": "golang.org/x/text/secure/bidirule",