Update run_instance.rb

We're using an aws-like service that does not support security groups. With this change a the DescribeSecurityGroups is only called if there are security groups.
Update docs on ELB support
Use a new class instead of a deprecated one
Update README.md

The documentation here is correct:
 http://docs.aws.amazon.com/cli/latest/reference/ec2/run-instances.html


If you specify aws.subnet_id and specify a list of security group names names for security_groups, then you will get the following error message:

==> default: Launching an instance with the following settings...
==> default:  -- Security Groups: ["A","B"]
...
==> default:  -- Assigning a public IP address in a VPC: false
There was an error talking to AWS. The error message is shown
below:

InvalidParameterCombination => The parameter groupName cannot be used with the parameter subnet


If you specify aws.subnet_id and specify a list of security group IDs names for security_groups, then this plugin works:

==> default: Launching an instance with the following settings...
==> default:  -- Security Groups: ["sg-1234","sg-4567"]
...
==> default:  -- Assigning a public IP address in a VPC: false
==> default: Waiting for instance to become "ready"...
==> default: Waiting for SSH to become available...
==> default: Machine is booted and ready for use!

See people talking about this here:
http://stackoverflow.com/questions/22365470/launching-instance-vpc-security-groups-may-not-be-used-for-a-non-vpc-launch
remove :endpoint option from elb config

When specifically setting an ec2 endpoint fog prints a warning when initializing the
`Fog::AWS::ELB` driver:

    [fog][WARNING] Unrecognized arguments: endpoint
Added retry delay when creating instances.

Without a retry delay - if you configure a lot of servers at the same time you will run into AWS API limits and it will throw an exception that will stop instance creation.

This adds in a minor delay when checking the status of an instance which seems to fix the issue when deploying ~ 20 - 40 machines.
Use the session token if it's available
Add support for the session token
Fix documentation
Use the vagrant SyncedFolders feature rather than using a custom one
Remove reference to old sync system
Merge pull request #322 from atlassian/destroy_unexisting

Handle "destroy" for non created machines properly
Merge pull request #320 from atlassian/rsync

Use the vagrant SyncedFolders feature rather than using a custom one
Merge pull request #297 from laurencer/master

Added retry delay when creating instances.
Merge pull request #292 from databus23/patch-1

remove :endpoint option from fog elb config
Merge pull request #270 from rosco5/patch-1

Improve documentation for aws.security_groups in a VPC
Merge pull request #264 from tatsuyafw/use-new-class-instead-of-deprecated-one

Use a new class instead of a deprecated one
Merge pull request #257 from dlouvton/patch-1

Update run_instance.rb
Merge pull request #315 from atlassian/session_token

Add support for session tokens
First cut of packaging