Refactor avoid twice parse

[antechrestos]

Fixes #692

Description

Based on @orisano work, this pull request completes his work by adding a unit test. I also rebased his work to get go.mod and integration tests in travis.

To do the unit test, I declared a private static variable that represents the stage loading. This variable is mocked during unit test and restored to its original value.

I also "privatized" calculateDependencies as it is not called elsewhere.

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• [x ] Includes unit tests
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Reviewer Notes

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

Release Notes
Avoid parsing Dockerfile twice during build.

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[antechrestos]

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[orisano]

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[antechrestos]

@tejal29 @cvgw the work done by @orisano looked great yet I encountered something unfortunate.
CalculateDependencies calls command_util.UpdateConfigEnv that will do some replacement on Env command.
This fonction will be called another time while the command execution as with this change it will be called on the same structure. On all example it will be ok, however, luckily there is a test Dockerfile_test_env that reveals this problem.
The command ENV test4="a\"b" gets replaced the first time and test4 is valued to a"b. So far, so good. Yet, the second time it gets called it fails:

error building image: error building stage: failed to execute command: failed to process "a"b": unexpected end of statement while looking for matching double-quote
breaking something else

Hence, either there is a way of flaging that environment replacement was done, or refactor calculateDependencies, or implement a Clone function in Stage complex structure, or simply close the two pull requests.

[antechrestos]

@tejal29 @cvgw any feedback? Just to know whether I should go deeper or close this pr (and let you close the twin one)

[tejal29]

@antechrestos Sorry. I havent had time to take a closer look at this.
IIUC, command_util.UpdateConfigEnv replaces only new environment variables set in cmd.Env.

I am not sure why the same env variable gets replaced twice. (unless a bug sneaked in)
Do you mind investigating that?

[antechrestos]

@tejal29 I will. It might lead to some change

[antechrestos]

Closed as #1174 was successfully merged