(maint) formatting

This removes trailing whitespaces in install_utils.rb
(QENG-1037) Install from git should accept depth

When installing from larger repositories, being able to specify depth can cut
the time of git checkout in half. This becomes especially helpful when you are
checking out multiple repositories.
Due to the older git on some of the templates, this provides the older
--branch name --depth 1 commands, which means when using depth, one should
ensure the rev passed is a branch and not a single commit. Alternatively one
can add depth_branch => 'name' to repository and have that used instead of rev.
(gh-426) Add prebuild packages to Dockerfile

Without this patch every time the specs run, prebuilt packages are
installed to the new docker image. Even when preserving the image.
To increase the speed of the test suite we install those packages when
creating the Docker image. The `HostPrebuiltSteps` checks whether those
are installed and does not do anything directly starting to execute the
specs inside the image.
Add Enterprise Linux (el)
(QENG-1033) combine two conditionals into a single statement
(QENG-1033) additional_pkgs should be a module level variable
(QENG-1033) Reset additional_pkgs in a way supported by all Ruby versions
(QENG-1033) Move all functionality into the Perf module and sync the rspec tests
(QENG-1033) Remove dead rspec code
Merge pull request #416 from anodelman/ec2

(MAINT) add ability to list all instances associated with an ec2 keyname
Merge pull request #439 from doug-rosser/perf_fixes

(QENG-1033) Don't modify constants and properly support all Linux platforms in Perf
Merge pull request #435 from leoc/add-prebuilt-packages-to-docker

(gh-426) Add prebuild packages to Dockerfile
Merge pull request #388 from ferventcoder/ticket/master/allow-git-depth

(QENG-1037) Install from git should accept depth
potential fix