Currently, the custom instance parameters (hv, be, nicp) are only
queryable via LUQueryInstanceData. LUQueryInstance returns only the
filled parameters, thus its users (especially RAPI) have no way to know
if a parameter is custom or the default value.

This patch adds three new parameters: custom_hvparams, custom_beparams,
custom_nicparams, that are also exported in RAPI.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>