Fixes trailing slash issue for namespaces

[petems]

• Currently the answer from the API returns a trailing slash
• Looking in other resources, we validate against having a trailing slash
• use filepath.Clean to trim trailing slash from API response
• Added test to delete resource so test could be run multiple times

Fixes #390

[petems]

Enterprise binary acceptance test:

$ vault-ent server -dev
==> Vault server configuration:

             Api Address: http://127.0.0.1:8200
                     Cgo: disabled
         Cluster Address: https://127.0.0.1:8201
              Listener 1: tcp (addr: "127.0.0.1:8200", cluster address: "127.0.0.1:8201", max_request_duration: "1m30s", max_request_size: "33554432", tls: "disabled")
               Log Level: info
                   Mlock: supported: false, enabled: false
                 Storage: inmem
                 Version: Vault v1.1.0+prem
             Version Sha: 385f51f541491d531c9bd986697d391523d70c3c

TF_ACC_ENTERPRISE=true make testacc
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test $(go list ./... |grep -v 'vendor') -v  -timeout 120m
=== RUN   TestNamespace_basic
--- PASS: TestNamespace_basic (0.06s)

2019-04-10T15:33:47.306+0100 [INFO]  core: successful mount: namespace=test-namespace-884024748716240442/ path=sys/ type=ns_system
2019-04-10T15:33:47.306+0100 [INFO]  core: successful mount: namespace=test-namespace-884024748716240442/ path=identity/ type=ns_identity
2019-04-10T15:33:47.306+0100 [INFO]  core: successful mount: namespace=test-namespace-884024748716240442/ path=cubbyhole/ type=ns_cubbyhole
2019-04-10T15:33:47.306+0100 [INFO]  core: enabled credential backend: path=token/ type=ns_token
2019-04-10T15:33:47.344+0100 [INFO]  core: disabled credential backend: path=auth/token/
2019-04-10T15:33:47.344+0100 [INFO]  core: successfully unmounted: path=cubbyhole/ namespace=test-namespace-884024748716240442/
2019-04-10T15:33:47.346+0100 [INFO]  core: successfully unmounted: path=identity/ namespace=test-namespace-884024748716240442/
2019-04-10T15:33:47.347+0100 [INFO]  core: successfully unmounted: path=sys/ namespace=test-namespace-884024748716240442/

[petems]

This is actually how it should be done, the API has it even documented that way 😄

	// Allowing writing to a path ending in / makes it extremely difficult to
	// understand user intent for the filesystem-like backends (kv,
	// cubbyhole) -- did they want a key named foo/ or did they want to write
	// to a directory foo/ with no (or forgotten) key, or...? It also affects
	// lookup, because paths ending in / are considered prefixes by some
	// backends. Basically, it's all just terrible, so don't allow it.
	if strings.HasSuffix(req.Path, "/") &&
		(req.Operation == logical.UpdateOperation ||
			req.Operation == logical.CreateOperation) {
		return logical.ErrorResponse("cannot write to a path ending in '/'"), nil
	}

https://github.com/hashicorp/vault/blob/8d15b09ed13423d206425ed070e3a72ebdba70b7/vault/request_handling.go#L430

[tyrannosaurus-becks]

Thanks @petems !