Extra config options for auth_backend

[martinssipenko]

Adds ability to configure following config parameters for auth_backend:

• default_lease_ttl_seconds
• max_lease_ttl_seconds
• listing_visibility
• local

Test output:

$ make testacc TESTARGS='-run=TestResourceAuth'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test $(go list ./... |grep -v 'vendor') -v -run=TestResourceAuth -timeout 120m
?       github.com/terraform-providers/terraform-provider-vault [no test files]
testing: warning: no tests to run
PASS
ok      github.com/terraform-providers/terraform-provider-vault/util    (cached) [no tests to run]
=== RUN   TestResourceAuth
--- PASS: TestResourceAuth (0.11s)
PASS
ok      github.com/terraform-providers/terraform-provider-vault/vault   0.139s

Fixes #203

[cvbarros]

This is a nicely needed improvement! I'm working on a new auth_backend resource and I've noted a few points:

IMO these auth backend resources need a bigger refactor, whereas the resource mounts/unmounts both the auth backend + configures its options.

Adding these configuration options to the "generic" resource auth_backend already increases this debt as put the newly created in fd5deed without these options.

IMHO, if still proceeding this PR, these options should also be added to the gcp_auth_backend plus any other auth backend resources that have the same approach.

[martinssipenko]

@cvbarros I agree, probably the best option would be a resource per each mount type (aws, gcp, github, etc).

The update (unmount/mount) part can be fixed using partial update and mount tune, similar to how it has been done in aws_secret_backend.

[martinssipenko]

@tyrannosaurus-becks given the above, I'm happy to add a new resource specifically for aws instead of amending the generic one. What's your view on this?

[kmcquade]

@martinssipenko @tyrannosaurus-becks @cvbarros - any chance you guys could also address the auth tune request here as well? See #234

[tyrannosaurus-becks]

@martinssipenko @cvbarros I am flexible on the approach around whether to add these parameters per-mount-type or onto the generic backend. This code is good to go so I don't want to create more work over it. Let's use it!

[tyrannosaurus-becks]

Thank you for noticing this and cleaning it up while you're at it.

[cvbarros]

@kmcquade There's an approach submitted in #255, which can be leveraged to all auth mounts regarding these options. Once that PR is discussed/merge I can happily extend it to other auth mounts as well