This PR adds a new Storage Backend for Triton's Object Storage - Manta
```
make testacc TEST=./physical/manta
==> Checking that code complies with gofmt requirements...
==> Checking that build is using go version >= 1.9.1...
go generate
VAULT_ACC=1 go test -tags='vault' ./physical/manta -v -timeout 45m
=== RUN TestMantaBackend
--- PASS: TestMantaBackend (61.18s)
PASS
ok github.com/hashicorp/vault/physical/manta 61.210s
```
Manta behaves differently to how S3 works - it has no such concepts of Buckets - it is merely a filesystem style object store
Therefore, we have chosen the approach of when writing a secret `foo` it will actually map (on disk) as foo/.vault_value
The reason for this is because if we write the secret `foo/bar` and then try and Delete a key using the name `foo` then Manta
will complain that the folder is not empty because `foo/bar` exists. Therefore, `foo/bar` is written as `foo/bar/.vault_value`
The value of the key is *always* written to a directory tree of the name and put in a `.vault_value` file.
* Use version to determine plugin protocol to use
* Remove field from ServeOpts
* Fix missing assignment, handle errors
* contraint -> constraint
* Inject the version string from the vault side
* Fix the version check
* Add grpc support check to database plugins
* Default to use grpc unless missing env var or fail on contraint check
* Add GRPCSupport test
* Add greater than test case
* Add go-version dep
* Add grpc plugins
* Add grpc plugins
* Translate wrap info to/from proto
* Add nil checks
* Fix nil marshaling errors
* Provide logging through the go-plugin logger
* handle errors in the messages
* Update the TLS config so bidirectional connections work
* Add connectivity checks
* Restart plugin and add timeouts where context is not availible
* Add the response wrap data into the grpc system implementation
* Add leaseoptions to pb.Auth
* Add an error translator
* Add tests for translating the proto objects
* Fix rename of function
* Add tracing to plugins for easier debugging
* Handle plugin crashes with the go-plugin context
* Add test for grpcStorage
* Add tests for backend and system
* Bump go-plugin for GRPCBroker
* Remove RegisterLicense
* Add casing translations for new proto messages
* Use doneCtx in grpcClient
* Use doneCtx in grpcClient
* s/shutdown/shut down/
* porting identity to OSS
* changes that glue things together
* add testing bits
* wrapped entity id
* fix mount error
* some more changes to core
* fix storagepacker tests
* fix some more tests
* fix mount tests
* fix http mount tests
* audit changes for identity
* remove upgrade structs on the oss side
* added go-memdb to vendor
