Add support for multiple values per key

[bwitt]

Summary

This is a clone of #481 to hopefully get it passing and merged.

This change adds support for ini files in which the same key is used multiple times for lists of values, for example:

[section]
foo=a
foo=b

To set multiple values, an array of values can be passed to the value property of ini_setting.

When passing a single value, the module works as before, with one exception: when a single value is passed to value, but the ini file already contains multiple lines with the same key, any additional lines will now be removed instead of retained.

Thanks to @omolenkamp for the original PR.

Additional Context

Add any additional context about the problem here.

• Root cause and the steps to reproduce. (If applicable)
• Thought process behind the implementation.

Related Issues (if any)

Fixes #41
Related to #481

Checklist

• 🟢 Spec tests.
• 🟢 Acceptance tests.
• Manually verified. (For example puppet apply)

[span786]

@bwitt Please resolve the conflicts.

[bwitt]

@span786 done!

[skyamgarp]

A PR has been created to execute tests for this contribution: #562

[skyamgarp]

A PR has been created to execute tests for this contribution: #562

@bwitt , can you please fix the failing specs?

[bwitt]

@skyamgarp I've added a fix, let me know how that looks!

[skyamgarp]

Tested against #562. Thank you @bwitt.