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/// @startDocuBlock JSF_cluster_test_GET
/// @brief executes a cluster roundtrip for sharding
///
/// @RESTHEADER{GET /_admin/cluster-test, Execute cluster roundtrip}
///
/// @RESTDESCRIPTION
///
/// Executes a cluster roundtrip from a coordinator to a DB server and
/// back. This call only works in a coordinator node in a cluster.
/// One can and should append an arbitrary path to the URL and the
/// part after */_admin/cluster-test* is used as the path of the HTTP
/// request which is sent from the coordinator to a DB node. Likewise,
/// any form data appended to the URL is forwarded in the request to the
/// DB node. This handler takes care of all request types (see below)
/// and uses the same request type in its request to the DB node.
///
/// The following HTTP headers are interpreted in a special way:
///
///   - *X-Shard-ID*: This specifies the ID of the shard to which the
///     cluster request is sent and thus tells the system to which DB server
///     to send the cluster request. Note that the mapping from the
///     shard ID to the responsible server has to be defined in the
///     agency under *Current/ShardLocation/<shardID>*. One has to give
///     this header, otherwise the system does not know where to send
///     the request.
///   - *X-Client-Transaction-ID*: the value of this header is taken
///     as the client transaction ID for the request
///   - *X-Timeout*: specifies a timeout in seconds for the cluster
///     operation. If the answer does not arrive within the specified
///     timeout, an corresponding error is returned and any subsequent
///     real answer is ignored. The default if not given is 24 hours.
///   - *X-Synchronous-Mode*: If set to *true* the test function uses
///     synchronous mode, otherwise the default asynchronous operation
///     mode is used. This is mainly for debugging purposes.
///   - *Host*: This header is ignored and not forwarded to the DB server.
///   - *User-Agent*: This header is ignored and not forwarded to the DB
///     server.
///
/// All other HTTP headers and the body of the request (if present, see
/// other HTTP methods below) are forwarded as given in the original request.
///
/// In asynchronous mode the DB server answers with an HTTP request of its
/// own, in synchronous mode it sends a HTTP response. In both cases the
/// headers and the body are used to produce the HTTP response of this
/// API call.
///
/// @RESTRETURNCODES
///
/// The return code can be anything the cluster request returns, as well as:
///
/// @RESTRETURNCODE{200}
/// is returned when everything went well, or if a timeout occurred. In the
/// latter case a body of type application/json indicating the timeout
/// is returned.
///
/// @RESTRETURNCODE{403}
/// is returned if ArangoDB is not running in cluster mode.
///
/// @RESTRETURNCODE{404}
/// is returned if ArangoDB was not compiled for cluster operation.
/// @endDocuBlock
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