Added capability to specify multiple services to update

[bfolkens]

Sometimes multiple services use the same task definition. It would be beneficial to have these deploy with the same version of the task definition, and within the same process, instead of having several different invocations of ecs-deploy making several versions of the same task definition.

Added the ability to specify multiple services through, for example:

-n "service-1 service-2 service-3"

[fillup]

@bfolkens this is an interesting new feature. I just merged in a couple PRs that will affect this one. Can you review and update based on #94 and #96? #96 will especially affect your changes as it adds auto-rollback if the new version does not deploy successfully.

[devon-sil]

Closing this since there have been no additional comments or changes since fillup's May 1, 2017 comment.