Prepend slash to service ID in DELETE

[xperimental]

There is a small discrepancy in the current bamboo version in handling the ID between PUT and DELETE.

Create service /some/service using PUT:

$ http -v PUT http://localhost:8000/api/services/some/service Id=/some/service "Acl=path_beg /some/service"
PUT /api/services/some/service HTTP/1.1
Accept: application/json
Accept-Encoding: gzip, deflate
Connection: keep-alive
Content-Length: 56
Content-Type: application/json
Host: localhost:8000
User-Agent: HTTPie/0.9.3

{
    "Acl": "path_beg /some/service",
    "Id": "/some/service"
}

HTTP/1.1 200 OK
Content-Length: 67
Content-Type: application/json
Date: Wed, 22 Jun 2016 16:47:50 GMT

{
    "Acl": "path_beg /some/service",
    "Config": null,
    "Id": "/some/service"
}

Delete same service:

> http -v DELETE http://localhost:8000/api/services/some/service
DELETE /api/services/some/service HTTP/1.1
Accept: */*
Accept-Encoding: gzip, deflate
Connection: keep-alive
Content-Length: 0
Host: localhost:8000
User-Agent: HTTPie/0.9.3



HTTP/1.1 400 Bad Request
Content-Length: 24
Content-Type: text/plain; charset=utf-8
Date: Wed, 22 Jun 2016 16:48:50 GMT
X-Content-Type-Options: nosniff

zk: node does not exist

This is because PUT and POST read the service-ID from the JSON payload and prepend a slash if the ID does not start with one. This fix just also adds the slash when using the DELETE request.

I noticed that there is also no input validation on the ID read from JSON, so if an empty string is passed it is converted to a single slash, which should probably also not happen.

[swagatha-christie]

By analyzing the blame information on this pull request, we identified @bluepeppers, @activars and @njuettner to be potential reviewers

[coveralls]

Coverage remained the same at 39.609% when pulling 21d8f39 on xperimental:prepend-slash into 7539277 on QubitProducts:master.

[j1n6]

LGTM. Thank you