build/release: Generate sha256sums for built binaries.

[harshavardhana]

Description

Generate sha256sums for built binaries. We used to build sha1sum deprecate it and use sha256sum instead.

Motivation and Context

Fixes #4306

How Has This Been Tested?

Manually using make release

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-io]

Codecov Report

Merging #4311 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4311      +/-   ##
==========================================
+ Coverage   66.61%   66.63%   +0.02%     
==========================================
  Files         176      176              
  Lines       25071    25071              
==========================================
+ Hits        16700    16707       +7     
+ Misses       7246     7238       -8     
- Partials     1125     1126       +1

Impacted Files	Coverage Δ
cmd/fs-v1-background-append.go	78.52% <0%> (-2.69%)	⬇️
cmd/posix.go	73.25% <0%> (-0.16%)	⬇️
cmd/update-notifier.go	75% <0%> (+21.42%)	⬆️

---

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[nitisht]

make release fails on macOS with

If you want to build for all, Just press Enter: linux/386
-->      linux/386:github.com/minio/minio
./buildscripts/build.sh: line 95: release/linux-386/minio.RELEASE.2017-05-10T03-27-55Z: cannot execute binary file

[harshavardhana]

./buildscripts/build.sh: line 95: release/linux-386/minio.RELEASE.2017-05-10T03-27-55Z: cannot execute binary file

Should work fine now.. used a more inter-operable tool.

[nitisht]

Should work fine now.. used a more inter-operable tool.

Works