update julia packages on running instances

Updates to Julia packages and user home image are now delivered through S3
and will not require creating a new AWS image any more.

Images are built and provisioned on S3 from any build machine.

Latest configured image is pulled on startup of a new ec2 instance and periodically on all
running ec2 instances.
Merge pull request #146 from tanmaykm/tanmaykm

update julia packages on running instances