sdk: combine RequestError detail only if response body not empty
sdk: combine RequestError detail only if response body not empty

Change-Id: I396a6ae2434abcb30662d6d985398e7af71fbf19
Signed-off-by: Michael Pasternak <af5566a40fc9757136fd9da9ca5e2dbdd9b039eb@redhat.com>

DragonRoman/ovirt-engine-sdk,DragonRoman/ovirt-engine-sdk,DragonRoman/ovirt-engine-sdk