Fixing issue where an invoke in the test was not being executed

[#157010541](https://www.pivotaltracker.com/story/show/157010541)

Author: xtreme-jason-smith

spec/integration/build/azure_spec.rb

@@ -63,6 +63,8 @@
         agent_commit
       )
 
+      # This allows the task to be ran multiple times by different tests
+      Rake::Task['build:azure'].reenable
       Rake::Task['build:azure'].invoke
 
       expect(File.read(File.join(@output_directory, "bosh-stemcell-#{version}-azure-vhd-uri.txt"))).to eq 'some-disk-image-url'

spec/tasks/build/azure_rake_spec.rb

@@ -29,8 +29,7 @@
     let(:env_var) { 'some_env_var' }
 
     before do
-      # This allows the task to be ran multiple times in the same context.
-      # If it's missing, then the task will only run one by the first test
+      # This allows the task to be ran multiple times in different tests.
       task.reenable
 
       allow(Stemcell::Builder).to receive(:validate_env).with(any_args)