* relax requirements for auto_encrypt on server
* better error message when auto_encrypt and verify_incoming on
* docs: explain verify_incoming on Consul clients.
This PR introduces reloading tls configuration. Consul will now be able to reload the TLS configuration which previously required a restart. It is not yet possible to turn TLS ON or OFF with these changes. Only when TLS is already turned on, the configuration can be reloaded. Most importantly the certificates and CAs.
This PR is based on #5366 and continues to centralise the tls configuration in order to be reloadable eventually!
This PR is another refactoring. No tests are changed, beyond calling other functions or cosmetic stuff. I added a bunch of tests, even though they might be redundant.
In order to be able to reload the TLS configuration, we need one way to generate the different configurations.
This PR introduces a `tlsutil.Configurator` which holds a `tlsutil.Config`. Afterwards it is responsible for rendering every `tls.Config`. In this particular PR I moved `IncomingHTTPSConfig`, `IncomingTLSConfig`, and `OutgoingTLSWrapper` into `tlsutil.Configurator`.
This PR is a pure refactoring - not a single feature added. And not a single test added. I only slightly modified existing tests as necessary.
The list of cipher suites included in this commit are consistent with
the values and precedence in the [Golang TLS documentation](https://golang.org/src/crypto/tls/cipher_suites.go).
> **Note:** Cipher suites with RC4 are still included within the list
> of accepted values for compatibility, but **these cipher suites are
> not safe to use** and should be deprecated with warnings and
> subsequently removed. Support for RC4 ciphers has already been
> removed or disabled by default in many prominent browsers and tools,
> including Golang.
>
> **References:**
>
> * [RC4 on Wikipedia](https://en.wikipedia.org/wiki/RC4)
> * [Mozilla Security Blog](https://blog.mozilla.org/security/2015/09/11/deprecating-the-rc4-cipher/)
* Upgrades to Go 1.7 and fixes vet finding and TLS behavior change.
* Fixes unit tests in a better manner by closing the client connection on errors.
We traced through and realized that https://github.com/golang/go/issues/15709
causes the output from the client to get buffered, which cuts off the alert
feedback due to the flush() call getting bypassed by the error return.
Chris Piraino