Initial addition of 9p code to Podman

This includes two new hidden commands: a 9p server,
`podman machine server9p`, and a 9p client,
`podman machine client9p` with `server9p` currently only
configured to run on Windows and serve 9p via HyperV vsock, and
`client9p` only configured to run on Linux. The server is run by
`podman machine start` and has the same lifespan as gvproxy
(waits for the gvproxy PID to die before shutting down). The
client is run inside the VM, also by `podman machine start`, and
mounts uses kernel 9p mount code to complete the mount. It's
unfortunately not possible to use mount directly without the
wrapper; we need to set up the vsock and pass it to mount as an
FD.

In theory this can be generalized so that the server can run
anywhere and over almost any transport, but I haven't done this
here as I don't think we have a usecase other than HyperV right
now.

[NO NEW TESTS NEEDED] This requires changes to Podman in the VM,
so we need to wait until a build with this lands in FCOS to test.

Signed-off-by: Matthew Heon <matthew.heon@pm.me>

vendor/github.com/u-root/uio/LICENSE

@@ -0,0 +1,29 @@
+BSD 3-Clause License
+
+Copyright (c) 2012-2021, u-root Authors
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright notice, this
+  list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright notice,
+  this list of conditions and the following disclaimer in the documentation
+  and/or other materials provided with the distribution.
+
+* Neither the name of the copyright holder nor the names of its
+  contributors may be used to endorse or promote products derived from
+  this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

vendor/github.com/u-root/uio/ulog/log.go

@@ -0,0 +1,31 @@
+// Copyright 2019 the u-root Authors. All rights reserved
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package ulog exposes logging via a Go interface.
+//
+// ulog has three implementations of the Logger interface: a Go standard
+// library "log" package Logger and a test Logger that logs via a test's
+// testing.TB.Logf. To use the test logger import "ulog/ulogtest".
+package ulog
+
+import "log"
+
+// Logger is a log receptacle.
+//
+// It puts your information somewhere for safekeeping.
+type Logger interface {
+	Printf(format string, v ...interface{})
+	Print(v ...interface{})
+}
+
+// Log is a Logger that prints to the log package's default logger.
+var Log Logger = log.Default()
+
+type emptyLogger struct{}
+
+func (emptyLogger) Printf(format string, v ...interface{}) {}
+func (emptyLogger) Print(v ...interface{})                 {}
+
+// Null is a logger that prints nothing.
+var Null Logger = emptyLogger{}