fix(Dockerfile): store kubectl and mc binary and download them on docker build

[arschles]

No description provided.

[arschles]

related to deis/dockerbuilder#2 and deis/slugbuilder#4

[arschles]

binaries stored at binary stored at https://storage.googleapis.com/alpine-binaries/mc and binary stored at https://storage.googleapis.com/alpine-binaries/kubectl

Update: these builds don't fully work with alpine linux

[arschles]

this will become a non-issue when either one of the following are true:

• The minio team publishes their official releases. This comment indicates that will be later this month.
• We complete the applicable part(s) of [Meta] consolidate into a single Go binary #29

We'll likely hit the first milestone before the second.

[arschles]

note that this issue will no longer apply for the mc binary because it's being completely removed in #106

[arschles]

also, this issue will no longer apply for kubectl because it's being completely removed in #115

[arschles]

Obsoleted by #133 (for kubectl) and #128 (for mc). Closing