Implement automatic port reassignment on Windows

While only leveraged by the WSL backend, this commit also adds core
infrastructure for all other backends for future enhancement.

- Adds a common port cross backend allocation registry to prevent duplicate
  assignment across multiple machine instances
- Introduces logic in Start() that detects OS port conflicts and scans for a
  viable replacement port
- Updates connection definitions and server configuration accordingly
- Utilizes a coordinated file lock strategy to prevent racing overwrites of port
  and connection registries
- WSL backend coordinates locking for containers.conf until a future common
  enhancement exists to replace it

[NO NEW TESTS NEEDED]

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

pkg/machine/ports_unix.go

@@ -0,0 +1,29 @@
+//go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd
+// +build darwin dragonfly freebsd linux netbsd openbsd
+
+package machine
+
+import (
+	"net"
+	"syscall"
+)
+
+func getPortCheckListenConfig() *net.ListenConfig {
+	return &net.ListenConfig{
+		Control: func(network, address string, c syscall.RawConn) (cerr error) {
+			if err := c.Control(func(fd uintptr) {
+				// Prevent listening socket from holding over in TIME_WAIT in the rare case a connection
+				// attempt occurs in the short window the socket is listening. This ensures the registration
+				// will be gone when close() completes, freeing it up for the real subsequent listen by another
+				// process
+				cerr = syscall.SetsockoptLinger(int(fd), syscall.SOL_SOCKET, syscall.SO_LINGER, &syscall.Linger{
+					Onoff:  1,
+					Linger: 0,
+				})
+			}); err != nil {
+				cerr = err
+			}
+			return
+		},
+	}
+}