set log format using a flag

[osela]

Fixes #1029

Description

This PR adds a log-format flag to make users' life easier when using log collectors like fluentd or in other scenarios where logs are parsed.
The flag supports 3 options:

• "text" - standard text format
• "color" - colored text format (default - to keep existing behavior)
• "json"

As part of the change I introduced a new logging package to hold all logic that deals with logging.

As the logic is mostly inside main I didn't find much value for unit tests, but I can add them if you insist :)

Submitter Checklist

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• Includes unit tests
• Adds integration tests if needed.

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Reviewer Notes

• The code flow looks good.
• Unit tests and or integration tests added.

Release Notes

Describe any changes here so maintainer can include it in the release notes, or delete this block.

- Add log-format flag

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[osela]

@googlebot I signed it!

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[tejal29]

@osela Please add bioler plate license code to newly added go file.

Thanks!

[tejal29]

2 small nit.

1. Add license to pkg/logging/logging.go
2. Add actionable error message.

[tejal29]

restarted the Travis build. Failed due to random docker install error.