By default, go get determines parallelism based on the number of
cores available. Those show up as 32 in the Travis CI environment
but a virtual machine is limited both by the amount of cores it
has allocated and the amount of memory available to it. 32 parallel
build processes are likely to exhaust the memory resources, leading
to killed processes.

This change reduces the number of builds running concurrently to 2,
which should reduce the likelihood of memory exhaustion greatly.

The number could probably be dialed up a little bit, but this should
give a good default reflecting the environment's resources.

(configs to disable will come next)

Config Dir and plugin discovery there

Merge branch '1064-fix-upload-file-permissions' of github.com:rasa/packer into rasa-1064-fix-upload-file-permissions

Conflicts:
	builder/parallels/common/step_upload_parallels_tools.go
	builder/vmware/common/step_upload_tools.go
	provisioner/chef-client/provisioner.go
	provisioner/chef-solo/provisioner.go

post-processor/compress Add support for artifact compression.

parallels-iso: allow absolute output directory.

Fixes [GH-1466]

Add the cleanup when the process of EBS AMI interrupted

Merge branch 'add-spot-instance-support' of github.com:henrysher/packer into henrysher-add-spot-instance-support

Conflicts:
	builder/amazon/common/run_config.go
	builder/amazon/ebs/builder.go
	builder/amazon/instance/builder.go

Conflicts:
	packer/config_template.go
	website/source/docs/templates/configuration-templates.html.markdown

common: Fixes #1114, Adds upper and lower as filters for the template engine.