Upgrade go-ucfg to v0.8.1 release

[blakerouse]

What does this PR do?

Updates the vendored go-ucfg to v0.8.1.

Note: This includes a breaking change that removes the variable substition from environment variables when they are read from the configuration. elastic/go-ucfg#139

Why is it important?

Gets the latest fixes and additions including:

Added

• Add support for HJSON. HJSON seems to not be implemented go-ucfg#131
• Add new parse.Config to adjust parsing of varibles returned by a Resolve. Fix parsing of environment variables to prevent object parsing. #132 go-ucfg#139
• Add call to InitDefaults when map, primitives, or structs implement Initializer interface during Unpack. Initialize defaults in sub-structures go-ucfg#104

Changed

• Moved internal/parse to parse module. Fix parsing of environment variables to prevent object parsing. #132 go-ucfg#139
• Add parse.Config to resolvers return. Fix parsing of environment variables to prevent object parsing. #132 go-ucfg#139

Fixed

• Prevent Validate from being called when value is a pointer or interface and is nil. Validate being called on structs that are nil go-ucfg#144
• Call Validate on custom slice types. The Validate method is not always called go-ucfg#133
• Call Validate on custom map types. More validator tests go-ucfg#136
• Disabled object parsing of environment variables. Fix parsing of environment variables to prevent object parsing. #132 go-ucfg#139
• Apply validation to defaults passed into Unpack when Config doesn't contain a value. Apply validators to default values go-ucfg#42

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works

Author's Checklist

• Does not break beats reading and parsing configuration files

How to test this PR locally

Related issues

Use cases

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Logs

[kvch]

The go-ucfg entries in vendor/vendor.json is not updated. Could you please update the dependency using govendor fetch? This way the NOTICE.txt file can be updated as well to reflect the versions/revisions we are using at the moment.

[kvch]

I meant updating all entries in the vendor.json, not just the top-level one. For example, github.com/elastic/go-ucfg/cfgutil, github.com/elastic/go-ucfg/flag, etc. Running govendor fetch github.com/elastic/go-ucfg/...@v0.8.1 would update everything.

[blakerouse]

@kvch I have used govendor and make notice to update the required files. I have also added the changelog entry and fixed the pull request description to link to the go-ucfg project pulls instead of old ones from beats.

[kvch]

The other packages from github.com/elastic/go-ucfg I have mentioned above are still not updated in vendor.json.

[blakerouse]

@kvch updated with govendor done correctly this time