Enable Windows CI (Appveyor)

- start list of linux_only plugins; ignore them when testing on Windows
- Isolate linux-only code by filename suffix
- Remove stub (NotImplemented) functions
- other misc. fixes for Windows compatibility

plugins/ipam/host-local/backend/disk/lock.go

@@ -1,3 +1,4 @@
+// +build !windows
 // Copyright 2015 CNI authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");

plugins/linux_only.txt

@@ -0,0 +1,11 @@
+plugins/host-device
+plugins/ipam/dhcp
+plugins/ipam/host-local
+plugins/main/bridge
+plugins/main/ipvlan
+plugins/main/loopback
+plugins/main/macvlan
+plugins/main/ptp
+plugins/main/vlan
+plugins/meta/portmap
+plugins/meta/tuning