Docker Build Enhancements
Docker Build Enhancements

This patch introduces two new environment variables for controlling
Docker builds:

* DLOCAL_IMPORTS  Specify a list of space-delimited import paths that
                  will be copied from the host OS's GOPATH into the
                  container build's vendor area, overriding the
                  dependency code that would normally be fetched by
                  Glide.

* DGLIDE_YAML     Specify a file that will be used for the container
                  build in place of the standard "glide.yaml" file. This
                  is necessary for occasions when sources injected into
                  the build via the DLOCAL_IMPORTS variable import
                  packages that are not imported by the package
                  specified in the project's standard "glide.yaml" file.
                  For example, if "glide.yaml" specifies that libStorage
                  depends upon AWS SDK v1.2.2, but DLOCAL_IMPORTS
                  specifies the value "github.com/aws/aws-sdk-go"
                  and the AWS SDK source code on the host includes a
                  new dependency not present in the v1.2.2 version,
                  Glide will not fetch the new AWS SDK dependency
                  when doing the container build. So it may be necessary
                  to use DGLIDE_YAML to provide a superset of the
                  project's standard "glide.yaml" file which also
                  includes the dependencies necessary to build the
                  packages specified in DLOCAL_IMPORTS.

Additionally, this patch also changes the default target for the
Makefile. If Docker is present and running on the localhost, executing
"make" will now execute the target "docker-build" instead of "deps" then
"build".

akutz/rexray,emccode/libstorage,thecodeteam/rexray,oppodeldoc/rexray,codedellemc/libstorage,oppodeldoc/rexray,thecodeteam/rexray,thecodeteam/rexray,codedellemc/libstorage,emccode/libstorage,MatMaul/libstorage,akutz/rexray,emccode/rexray,cduchesne/rexray,codedellemc/rexray,cduchesne/rexray,akutz/libstorage,MatMaul/libstorage,codedellemc/libstorage,akutz/rexray,codedellemc/libstorage,cduchesne/rexray,oppodeldoc/rexray,akutz/rexray,emccode/rexray,thecodeteam/rexray,cduchesne/rexray,codedellemc/libstorage,akutz/libstorage,akutz/libstorage,codedellemc/rexray,MatMaul/libstorage,emccode/libstorage,MatMaul/libstorage,codedellemc/rexray,MatMaul/libstorage,MatMaul/libstorage,codedellemc/rexray,cduchesne/rexray,cduchesne/rexray,thecodeteam/rexray,emccode/rexray,codedellemc/libstorage,akutz/libstorage,akutz/rexray,akutz/libstorage,oppodeldoc/rexray,emccode/libstorage,akutz/rexray,oppodeldoc/rexray,emccode/libstorage,codedellemc/rexray,emccode/libstorage,akutz/libstorage,codedellemc/rexray,oppodeldoc/rexray,thecodeteam/rexray,emccode/rexray