Accepts aws-sdk-java timestamp format

The aws-sdk-java timestamp format is "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"
which contains millisecond representation. However, the current
implementation does not accept this kind of format.

References:
https://github.com/aws/aws-sdk-java/blob/master/src/main/java/com/amazonaws/auth/QueryStringSigner.java#L173

Adds ability to parse this format in ec2utils.is_ec2_timestamp_expired.

Fixes bug 1156445.

Change-Id: I389ff8b9c6c91b699538b889add264d66dbb8131
Merge "Accepts aws-sdk-java timestamp format"