don't overwrite hook which has a same path

[liangchenye]

Signed-off-by: Liang Chenye [email protected]

[liangchenye]

The issue is found in #569.

For history reason, we add a hook and add hook env separately, so the 'path' is the unique ID to add env correctly. Now we are adding a full hook with json format, so we don't need to have this limitation.
Also, in the spec, it is OK to have hooks with the same 'path'.

[liangchenye]

PTAL @q384566678 @Mashimiao

[zhouhao3]

LGTM