Fixes security group handling for spot requests launching into a VPC on AWS
[openvz] Fixes #1871 test helper callback

This moves the setting up of an `at_exit` callback from when the file
is required to when the matching helper is used.

This prevents it failing on any run where OpenVZ is excluded.
[AWS | AutoScaling] Do not send Instances for update_auto_scaling_group
(Avoids 413 Request Entity Too Large for ASGs with lots of instances)
[AWS | Autoscaling] whitelist the options for update_auto_scaling_group
[AWS | Autoscaling] whitelist the options for create_auto_scaling_group
[AWS | Autoscaling] dry up expected options
[AWS | Autoscaling] correct whitelist for create_auto_scaling_group
[AWS | Autoscaling] ensure tests work in 1.8.7
Swapped to SecurityGroupId
[core] Removes unused getting of Constant
Merge pull request #1885 from fog/cleanup_cc69d10c

[core] Removes unused getting of Constant
Merge pull request #1874 from mikehale/asg-exclude-instances

[AWS | AutoScaling] Do not send Instances for update_auto_scaling_group
Merge pull request #1831 from contentfree/master

Fixes security group handling for spot instances launched into an EC2 VPC
fix create_tenant Mock response description and name

The attributes hash keys are all symbols. Please reference:
https://github.com/fog/fog/blob/master/lib/fog/core/attributes.rb#L20
Merge pull request #1889 from dmcinnes/patch-1

fix create_tenant Mock response description and name
[vcloud|compute] better defaults for configuring vm content-type

closes #1879
Update excon dependency to version ~>0.24.0
[core] Comments why Nokogiri 1.6 is not being used

The fog community decided to continue supporting Ruby 1.8.7 whilst
Nokogiri 1.6 drops support so ~> 1.5.0 is the correct version in
`fog.gemspec`.

See https://github.com/fog/fog/issues/1878 for more details.

[#1878]
Merge pull request #1891 from sferik/update_excon_dependency

Update excon dependency to version ~>0.24.0
Fix autoincrement when creating a flavor if private flavors exist.

Before, only public flavors were considered when finding the next free ID. That could lead to the case where the calculated ID was already taken which lead to a conflict. This happened whenever the user tried to create a private flavor via fog and then another (private OR public) flavor afterwards. Now, we also take private flavors into account, so the conflict cannot happen anymore.

As a side effect, it is now also possible to just return all private flavors, using the :is_public => false filter on the list_flavors_detail API call or the flavors collection.