OCM sharing fails when reva is configured to use users json file

[redblom]

#3526 introduces a new owner parameter format (opaqueId@webDAVHost) in the share request for the ocm share nextcloud driver. The ocmd shares service at the receiving end will try to parse this owner value into the user opaqueID and the webDAV host again.
But this is not implemented for the ocm share json driver. So when reva is configured to use the users json file sharing fails 'in panic' due to an index out of range error.

[redblom]

So basically changing:

reva/pkg/ocm/share/manager/json/json.go

Line 271 in 2a74f67

"owner": userID.OpaqueId,

into:
"owner": fmt.Sprintf("%s@%s", userID.OpaqueId, userID.Idp),

as stated here:

reva/pkg/ocm/share/manager/json/json.go

Line 273 in 2a74f67

"meshProvider": userID.Idp, // FIXME: move this into the 'owner' string?

should do the trick.

[redblom]

Fixed with #3551