Fixed JERSEY-1845.

- Interceptor stream closed properly after read if not cleaned-up by the interceptor.
- Added reproducer test.
- Minor refactoring of EntityContent.

Change-Id: Ifabec9e1df3b600f45fe041ceb243ff88f5dc427
Signed-off-by: Marek Potociar <marek.potociar@oracle.com>