Add advanced secret management

**What**
- Add the ability to specify secrets as a csv
- Vendor the docker/cli/opts
- Update the guide for secrets to use the `faas-cli`

**Why**
- Allowing the csv specification of secrets gives users more control about how
those secrets are mounted into the container.  This is good for things like
key rotation and for developers that are building on top of OpenFaaS.

Signed-off-by: Lucas Roesler <lucas.roesler@gmail.com>

gateway/vendor/github.com/docker/cli/README.md

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+[![build status](https://circleci.com/gh/docker/cli.svg?style=shield)](https://circleci.com/gh/docker/cli/tree/master)
+
+docker/cli
+==========
+
+This repository is the home of the cli used in the Docker CE and
+Docker EE products.
+
+It's composed of 3 main folders
+
+* `/cli` - all the commands code.
+* `/cmd/docker` - the entrypoint of the cli, aka the main.
+
+Development
+===========
+
+### Build locally
+
+```
+$ make build
+```
+
+```
+$ make clean
+```
+
+You will need [gox](https://github.com/mitchellh/gox) for this one:
+
+```
+$ make cross
+```
+
+If you don't have [gox](https://github.com/mitchellh/gox), you can use the "in-container" version of `make cross`, listed below.
+
+### Build inside container
+
+```
+$ make -f docker.Makefile build
+```
+
+```
+$ make -f docker.Makefile clean
+```
+
+```
+$ make -f docker.Makefile cross
+```
+
+### In-container development environment
+
+```
+$ make -f docker.Makefile dev
+```
+
+Then you can use the [build locally](#build-locally) commands:
+
+```
+$ make build
+```
+
+```
+$ make clean
+```
+
+Legal
+=====
+*Brought to you courtesy of our legal counsel. For more context,
+please see the [NOTICE](https://github.com/docker/cli/blob/master/NOTICE) document in this repo.*
+
+Use and transfer of Docker may be subject to certain restrictions by the
+United States and other governments.
+
+It is your responsibility to ensure that your use and/or transfer does not
+violate applicable laws.
+
+For more information, please see https://www.bis.doc.gov
+
+Licensing
+=========
+docker/cli is licensed under the Apache License, Version 2.0. See
+[LICENSE](https://github.com/docker/docker/blob/master/LICENSE) for the full
+license text.