[capi] Change the user_space_wrappers capi interface to return error codes when a core is not found.
[capi] Change the user_space_wrappers capi interface to return error codes when a core is not found.

nkawahara/Graphite,8l/Graphite,8l/Graphite,nkawahara/Graphite,mit-carbon/Graphite-Cycle-Level,fhijaz/Graphite,mit-carbon/Graphite,fhijaz/Graphite,fhijaz/Graphite,8l/Graphite,mit-carbon/Graphite-Cycle-Level,nkawahara/Graphite,nkawahara/Graphite,mit-carbon/Graphite,victorisildur/Graphite,victorisildur/Graphite,victorisildur/Graphite,fhijaz/Graphite,mit-carbon/Graphite-Cycle-Level,8l/Graphite,mit-carbon/Graphite,mit-carbon/Graphite-Cycle-Level,victorisildur/Graphite,mit-carbon/Graphite