Correctly index SecurityGroupId parameter when it is inside a NetworkInterfaces hash.
Fix issue #2796 (AWS describe_dhcp_options request parsing)

Properly initialize @dhcp_options for each dhcpOptionsSet
Merge pull request #2788 from kthakar/run-instances

Correctly index SecurityGroupId parameter
Merge pull request #2797 from knatsakis/master

Fix issue #2796 (AWS describe_dhcp_options request parsing)