Upgraded AWS API version to 2014-10-01 (latest)

 * All EC2 requests now use the latest AWS API version available (2014-10-01).
 * ec2test server response types changed as needed to mimic EC2 better (proper response type names and xmlns added).
 * IPPerms.SourceIPs changed from []string to []SourceIP. This is needed because SourceIPs was declared as serializable to "xml:ipRanges>item>cidrIp", which is wrong because it does not allow setting more than one source IP (e.g.`<ipRanges><item><cidrIp>1.2.3.4</cidrIp></item><item><cidrIp>4.3.2.1</cidrIp></item></ipRanges>` as expected by EC2 vs. `<ipRanges><item><cidrIp>1.2.3.4</cidrIp><cidrIp>4.3.2.1</cidrIp></item></ipRanges>` as it was before, which is not valid).
 * Added ec2.SourceIPs() helper to ease the transition between []string and []SourceIP.
 * Changed ec2test responses and tests to match EC2 in a few cases (e.g. InvalidGroup.InUse -> DependencyViolation)
 * Removed CreateSecurityGroupVPC() and changed CreateSecurityGroup() to take a VPC ID as first argument (can be empty to create an EC2-Classic SG or a valid VPC ID to create an EC2-VPC SG).
 * When debug=true, requests and responses are dumped to the log output. Requests are formatted similarly to the way AWS API docs does).
 * Added a few fields to the Instance type - AssociatePublicIP, EbsOptimized, SRIOVNetSupport - available in more recent AWS API versions.
 * Improved tests logging and stability when running against live EC2 servers.