ec2: support RunInstances with BlockDeviceMappings
Support security groups in instance responses at the instance level as well as at the reservation level
Support instance prefix on group-name and group-id instance filters
ec2: Support groups at instance and reservation

Per the 2011-12-15 wsdl description of the EC2 api, the
GroupSetType containing security group details appears
on both ReservationInfoType and RunningInstancesSetType
inside it.

This branch updates the code to parse the details at both
levels in a RunInstances or DescribeInstances response,
and updates the mock server to return the same details
at both levels.

Change is required as it seems the reservation group set
is empty, while the instance group set is not in some
circumstances.

R=rog
CC=
https://codereview.appspot.com/14302043
ec2: support instance prefix on group filters

The EC2 API documentation allows for alternative spellings of
the group-name and group-id filters on instances. It seems only
the prefixed forms are actually supported when using default VPC
despite claims to the contrary, so add support for them to the
test server infrastructure.

R=rog
CC=
https://codereview.appspot.com/14304043
Merged from trunk.
ec2: support RunInstances with BlockDeviceMappings

R=dfc, nate.finch
CC=
https://codereview.appspot.com/9860044
Merge branch 'bzr/goamz'