[aws|compute] added security group get by id method

lib/fog/aws/models/compute/security_groups.rb

@@ -88,6 +88,28 @@ module Fog
           end
         end
 
+        # Used to retreive a security group
+        # group id is required to get the associated flavor information.
+        #
+        # You can run the following command to get the details:
+        # AWS.security_groups.get_by_id("default")
+        #
+        # ==== Returns
+        #
+        #>> AWS.security_groups.get_by_id("sg-123456")
+        #  <Fog::AWS::Compute::SecurityGroup
+        #    name="default",
+        #    description="default group",
+        #    ip_permissions=[{"groups"=>[{"groupName"=>"default", "userId"=>"312571045469"}], "fromPort"=>-1, "toPort"=>-1, "ipRanges"=>[], "ipProtocol"=>"icmp"}, {"groups"=>[{"groupName"=>"default", "userId"=>"312571045469"}], "fromPort"=>0, "toPort"=>65535, "ipRanges"=>[], "ipProtocol"=>"tcp"}, {"groups"=>[{"groupName"=>"default", "userId"=>"312571045469"}], "fromPort"=>0, "toPort"=>65535, "ipRanges"=>[], "ipProtocol"=>"udp"}],
+        #    owner_id="312571045469"
+        #  > 
+        #
+        
+        def get_by_id(group_id)
+          if group_id
+            self.class.new(:connection => connection).all('group-id' => group_id).first
+          end
+        end
       end
 
     end