(TK-103) Reworked sync single request APIs to create and close client

For both the Clojure and Java single request APIs, the internal
implementation now creates an http client, makes a request on it, and
calls close on the client when done.  The close at the end avoids
resource leaks.

In support of this, the `JavaClient` class now requires the caller to
create an instance rather than just make a call to the static
`request` method on the `JavaClient` class.

The `coerceBodyType` method on the `JavaClient` class now closes the
body `InputStream` after coercing the stream content into a `String`.
This eliminates a possible resource leak and makes the Java-layer
coerce implementation consistent with the Clojure-layer coerce in
that the latter was already, via the use of the Clojure `slurp`
function, closing the stream content after coercing to `String`.