aws: Add TimeUnixMilli utility func
aws: Add TimeUnixMilli utility func

Adds a new utility function, TimeUnixMilli which takes the given time
value and returns the int64 time in milliseconds from epoc (January 1,
1970 UTC)

This can be used with APIs such as CloudWatch Logs which require their unix
time to be provided as milliseconds instead of the built in Go's nano or
second values.

Fix #686

radeksimko/aws-sdk-go,jjeffery/aws-sdk-go,yxd-hde/aws-sdk-go,radeksimko/aws-sdk-go,calgaryscientific/aws-sdk-go,calgaryscientific/aws-sdk-go,zmarois/aws-sdk-go,zmarois/aws-sdk-go,xibz/aws-sdk-go,jjeffery/aws-sdk-go,zmarois/aws-sdk-go,yxd-hde/aws-sdk-go,myshen/aws-sdk-go,yxd-hde/aws-sdk-go,agworld/aws-sdk-go,jjeffery/aws-sdk-go,radeksimko/aws-sdk-go,agworld/aws-sdk-go,yxd-hde/aws-sdk-go,zmarois/aws-sdk-go,radeksimko/aws-sdk-go,xibz/aws-sdk-go,myshen/aws-sdk-go,calgaryscientific/aws-sdk-go,xibz/aws-sdk-go,calgaryscientific/aws-sdk-go,jasdel/aws-sdk-go,myshen/aws-sdk-go,agworld/aws-sdk-go,aws/aws-sdk-go,xibz/aws-sdk-go,agworld/aws-sdk-go,myshen/aws-sdk-go