Support uri unsafe characters in proxy_uri

Allow the user to use unsafe characters (@, :, / for instance) in the proxy_uri through the use of URI::decode for the username and password components of the URI. 

This change is particularly critical for users of proxies with Windows domain style (domain/user) usernames.
Replace UUIDTools with SecureRandom.uuid
Backport SecureRandom.uuid for Ruby 1.8.7
Update hosted_zone_collection.rb

updated the documentation to reflect that you need to use the ID.
Fix a performance issue when calling CredentialProviders::DefaultProvider#credential. Using nil check instead of raise rescue exception for control flow, because using exception is super slow when stack trace is reasonably deep.
fix vault.archives account_id
Introduce Provider#set? to credential providers' interface and let Provider#credentials method continue to raise MissingCredentialsError when credentials are not set. This way we can make Provider's public interface backwards-compatible.
Added a :connection_pool option to NetHttpHandler to allow the pool to be injected.

Also added a ConnectionPool.build method that contructs an unmanged pool.
Fixed an RDS client bug, requiring :db_security_group_name for #authorize_db_security_group_ingress.
Bump version to v1.36.2
Updated AWS::OpsWorks::Client to support the latest API version.
Updated AWS::CloudFormation::Client API docs.
Updated AWS::ELB::Client to support connection draining.
Updated AWS::Kinesis::Client API documentation.
Bump version to v1.37.0
Added support to AWS::CloudSearch for the 2013-01-01 API version.
Updated AWS::Redshift API model.
Added support to AWS::EC2 for the 2014-02-01 API version.
Bump version to v1.38.0
adding placement_group option for instance creation