* add TencentCloud COS backend for remote state

* add vendor of dependence

* fixed error not handle and remove default value for prefix argument

* get appid from TF_COS_APPID environment variables

This mirrors the change made for providers, so that default values can
be inserted into the config by the backend implementation. This is only
the interface and method name changes, it does not yet add any default
values.

In order to support free organizations, we need a way to load the `remote` backend and then, depending on the used offering/plan, enable or disable remote operations.

In other words, we should be able to dynamically fall back to the `local` backend if needed, after first configuring the `remote` backend.

To make this works we need to change the way this was done previously when the env var `TF_FORCE_LOCAL_BACKEND` was set. The clear difference of course being that the env var would be available on startup, while the used offering/plan is only known after being able to connect to TFE.

This is a refactored version of the `remote` backend that was initially added to Terraform v0.11.8 which should now be compatible with v0.12.0.

This work was done against APIs that were already changed in the branch
before work began, and so it doesn't apply to the v0.12 development work.

To allow v0.12 to merge down to master, we'll revert this work out for now
and then re-introduce equivalent functionality in later commits that works
against the new APIs.

It’s a purely cosmetic change, but I find it easier to read them like this.

This PR changes manta from being a legacy remote state client to a new backend type. This also includes creating a simple lock within manta

This PR also unifies the way the triton client is configured (the schema) and also uses the same env vars to set the backend up

It is important to note that if the remote state path does not exist, then the backend will create that path. This means the user doesn't need to fall into a chicken and egg situation of creating the directory in advance before interacting with it

Alert users to use the current "azurerm" naming.

This is a simple wrapper to allow a backend to be marked as deprecated
during initialization.

Added locking support via blob leasing (requires that an empty state is
created before any lock can be acquired.

Added support for "environments" in much the same way as the S3 backend.

Move the Swift State from a legacy remote state to an official backend.
Add `container` and `archive_container` configuration variables, and deprecate `path` and `archive_path` variables.

Future improvements: Add support for locking and environments.

Move the S3 State from a legacy remote state to an official backend.

This increases test coverage, uses a set schema for configuration, and
will allow new backend features to be implemented for the S3 state, e.g.
"environments".