Bump aws-sdk to v1.57.0 for eu-central-1 support

Prior to this commit, we pinned aws-sdk to v1.42.0. Today, AWS brought
the eu-central-1 datacenter online. When Beaker attempts to run its
zombie killer script(s), the AWS SDK doesn't know how to handle this
datacenter. To combat the issue, AWS released v1.57.0 of the aws-sdk gem
today to coincide with this datacenter being brought online.

This commit modifies Beaker's Gemspec to use aws-sdk v1.57.0 so that it
can properly use the eu-central-1 datacenter.
(QENG-1414) Allow installation of OSX using simplified agent

OSX has been a supported simplified platform since its release, but
beaker did not support this deployment pattern. This change makes it
work.

Conflicts:
	lib/beaker/dsl/install_utils.rb
Merge pull request #506 from puppetlabs/aws-sdk-bump

Bump aws-sdk to v1.57.0 for eu-central-1 support
Merge pull request #507 from branan/osx_simplified_support

(QENG-1414) Allow installation of OSX using simplified agent
(QENG-1400) Added support for host operations on a mac
(QENG-1400) Allowed yield blocks to get at actual command output, and returned unix style passwd user output

Mac's dscl output isn't formatted as the /etc/passwd expected by callers.  In order to go back to this, I changed the yield to use the
information after I formatted it.  However, this fails because the callers are relying on the parameter given to them having a .stdout
call and other things like it, so I've gone back to that old way, and allowed the unix formatting to still be used in the return