Bump Go to 1.16

[ccarlfjord]

What this PR does / why we need it:

• Bumps go to 1.16, mitigating https://github.com/golang/go/issues/37436
• Uses go install instead of go get for installing build tools.

  go install now accepts arguments with version suffixes (for example, go install example.com/cmd@v1.0.0). This causes go install to build and install packages in module-aware mode, ignoring the go.mod file in the current directory or any parent directory, if there is one. This is useful for installing executables without affecting the dependencies of the main module. source

[coveralls]

Coverage remained the same at 19.481% when pulling c00f7f06060dcbb1168c4bd4da986f742f7d977e on ccarlfjord:go1.16 into 4e6e50fbc25b299e573fccec2b01cbab57726c18 on jtblin:master.