Stub out ReadPassword on plan9 and solaris to fix compilation

fs/config_read_password_unsupported.go

@@ -0,0 +1,12 @@
+// ReadPassword for OSes which are not supported by golang.org/x/crypto/ssh/terminal
+// See https://github.com/golang/go/issues/14441 - plan9
+//     https://github.com/golang/go/issues/13085 - solaris
+
+// +build solaris plan9
+
+package fs
+
+// ReadPassword reads a password with echoing it to the terminal.
+func ReadPassword() string {
+	return ReadLine()
+}