jsonrpc: Stomp client fails for multi frame messages without ssl

When ssl is set to false and there are multiple network frames for
single message the code didn't handled that case properly and failed
during parsing json. The same issue was when message size was greater
than buffer size. Encoding improvements where added to the patch.

Bug-Url: https://bugzilla.redhat.com/1115152
Change-Id: I96f38b6f4560fa57a4a5a2af436dd17653ff4cc8
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>