Update support for go 1.12 (also triggers some file reformatting)

[sjmudd]

Orchestrator build fails on go1.12 so adjust.

[user@host ~/src/orchestrator/src/github.com/github/orchestrator]$ go version
go version go1.12 darwin/amd64
[user@host ~/src/orchestrator/src/github.com/github/orchestrator]$ ./build.sh -b
Build only; no packaging
go version must be between 1.8 and 1.10

This also triggers some file reformatting (due to go fmt changes) which I've included.
There are no functional changes in the code.

• contributed code is using same conventions as original code
• code is formatted via gofmt (please avoid goimports)
• code is built via ./build.sh

[sjmudd]

Related: #857.

[shlomi-noach]

@sjmudd thank you. Can you please also remove go1.8, and update the .travis.yml file?

[shlomi-noach]

Because go1.12 has different formatting than previous versions, go1.12 will be the minimal supported version. I don't wish to support both 1.11 and 1.12 with differing formatting.

[shlomi-noach]

Added:

• using go1.12 on Travis
• using go1.12 in Docker
• Updated script/ensure-go-installed