fix for run_instances, make ec2 raise errors again

lib/fog/aws/ec2.rb

@@ -51,7 +51,6 @@ require "#{requests_directory}/revoke_security_group_ingress"
 require "#{requests_directory}/run_instances"
 require "#{requests_directory}/terminate_instances"
 
-
 module Fog
   module AWS
     class EC2
@@ -116,7 +115,7 @@ module Fog
 
         response = @connection.request({
           :body => body,
-          # :expects => 200,
+          :expects => 200,
           :headers => { 'Content-Type' => 'application/x-www-form-urlencoded' },
           :host => @host,
           :method => 'POST',

lib/fog/aws/requests/ec2/run_instances.rb

@@ -66,7 +66,7 @@ module Fog
           'ImageId' => image_id,
           'MinCount' => min_count,
           'MaxCount' => max_count,
-          'AvailabilityZone' => options[:availability_zone],
+          'Placement.AvailabilityZone' => options[:availability_zone],
           'Data' => options[:data],
           'DeviceName' => options[:device_name],
           'Encoding' => options[:encoding],