Fix CondOp JSON rendering for nullary conditional operators

AttributeValueList must only be rendered when it is to contain at least
one element. Rendering an empty AttributeValueList will result in a 500
error; this occurs when using a nullary conditional operator such as
IsNull or NotNull.
Merge pull request #127 from alephcloud/fix/conditional-writes

Fix CondOp JSON rendering for nullary conditional operators
regenerate aws.nix
Merge pull request #131 from alephcloud/dynamodb-test-suite

Dynamodb test suite
add time prefix to all test resources
add more debug output to help find dynamodb issue
tests/Utils.hs: add function 'mustFail'
tests/Sqs/Main.hs: add function SqsT to run requests with a given manager and base configuration
tests/DynamoDb/Utils.hs: add function dyT to run requests with a given manager and base configuration
tests/DynamoDb: add test case for reuse of TCP connections
tests/Sqs: add test case for reuse of TCP connections
DynamoDb: trigger reuse of TCP connection by forcing endOfInput in ResponseConsumer