Use alpine to build wasmd docker image

[ethanfrey]

Depends on CosmWasm/wasmvm#106

Uses a alpine compiler docker image (from go-cosmwasm) to build a static lib from go-cosmwasm, the compile it to a static go binary. After this is completed, copy the wasmd and wasmcli binaries into a minimal alpine image along with the helper scripts we use in CI (cosmjs) testing.

• Targeted PR against correct branch (see CONTRIBUTING.md)

• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added relevant godoc comments.

• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md

• Re-reviewed Files changed in the Github PR explorer

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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov-commenter]

Codecov Report

Merging #139 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #139   +/-   ##
=======================================
  Coverage   61.99%   61.99%           
=======================================
  Files          20       20           
  Lines        1768     1768           
=======================================
  Hits         1096     1096           
  Misses        578      578           
  Partials       94       94           

Impacted Files	Coverage Δ
x/wasm/internal/keeper/keeper.go	86.32% <100.00%> (ø)

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