Complete WSL implementation, refactor a few areas

Also addresses a number of issues:
- StopHostNetworking isn't plumbed, win-sshproxy leaks on hyperv
- Wait api and print output doesn't work properly on Windows
- API forwarding doesn't work on WSL
- Terminal corruption with after start/stop on Windows
- Gvproxy is forcefully killed vs gracefully quit
- Switching rootful/rootless does not update /var/run/docker.sock on the guest
- File already closed error on init
- HyperV backend is publishing Unix sockets when it should be named pipes
- User-mode networking doesn't always work
- Stop state outside of lock boundaries
- WSL blocks parallel machined (should be supported)

[NO NEW TESTS NEEDED]

Signed-off-by: Jason T. Greene <jason.greene@redhat.com>

pkg/machine/machine_unix.go

@@ -3,7 +3,10 @@
 package machine
 
 import (
+	"context"
 	"errors"
+	"fmt"
+	"net"
 	"strings"
 )
 
@@ -32,3 +35,11 @@ func ParseVolumeFromPath(v string) (source, target, options string, readonly boo
 	}
 	return
 }
+
+func DialNamedPipe(ctx context.Context, path string) (net.Conn, error) {
+	return nil, errors.New("not implemented")
+}
+
+func GetEnvSetString(env string, val string) string {
+	return fmt.Sprintf("export %s='%s'", env, val)
+}