Fixed failing members import tests

refs TryGhost@05f6faf

- The logic in "Stripe" error detection depended on error's message string matching, which is not a good practice in general. Had fixed it do to exact match on "context" of the error we throw internally and left more extensive comment about why things are implemented the way they are.

core/server/api/canary/members.js

@@ -231,8 +231,10 @@ const members = {
                     });
                 }
 
-                // NOTE: failed to link Stripe customer/plan/subscription
-                const isStripeLinkingError = error.message && error.message.match(/customer|plan|subscription|Stripe account/g);
+                // NOTE: failed to link Stripe customer/plan/subscription or have thrown custom Stripe connection error.
+                //       It's a bit ugly doing regex matching to detect errors, but it's the easiest way that works without
+                //       introducing additional logic/data format into current error handling
+                const isStripeLinkingError = error.message && (error.message.match(/customer|plan|subscription/g) || error.context === i18n.t('errors.api.members.stripeNotConnected.context'));
                 if (model && isStripeLinkingError) {
                     if (error.message.indexOf('customer') && error.code === 'resource_missing') {
                         error.message = `Member not imported. ${error.message}`;