Address suggestions from last code review

Rename method and update specs.

ee/app/services/gitlab_subscriptions/create_lead_service.rb

@@ -3,7 +3,7 @@
 module GitlabSubscriptions
   class CreateLeadService
     def execute(company_params)
-      response = subscription_app_client.create_trial_account(company_params)
+      response = subscription_app_client.generate_trial(company_params)
 
       if response.success
         { success: true }

ee/lib/gitlab/subscription_portal/client.rb

@@ -3,7 +3,7 @@
 module Gitlab
   module SubscriptionPortal
     class Client
-      def create_trial_account(params)
+      def generate_trial(params)
         parse_response(Gitlab::HTTP.post("#{base_url}/trials",
                                          body: params.to_json,
                                          headers: headers))

ee/spec/lib/gitlab/subscription_portal/client_spec.rb

@@ -8,7 +8,7 @@ describe Gitlab::SubscriptionPortal::Client do
     let(:httparty_response) { double(code: http_response.code, response: http_response, body: {}.to_json) }
 
     subject do
-      described_class.new.create_trial_account({})
+      described_class.new.generate_trial({})
     end
 
     context 'when response is successful' do
@@ -31,7 +31,7 @@ describe Gitlab::SubscriptionPortal::Client do
       end
     end
 
-    context 'when response code is generic' do
+    context 'when response code is 500' do
       let(:http_response) { Net::HTTPServerError.new(1.0, '500', 'Error') }
 
       it 'has a server error status' do