Adding a merge_all function to slsutil

[onlyanegg]

The merge_all function merges a list of objects in order. This will make merging multiple objects more readable. Consider the difference between merging three objects with slsutil.merge versus merging with slsutil.merge_all

With slsutil.merge:

{{ hadoop.hdfs.data_node.service.name }}_environment_file_installed:
  file.managed:
    - name: /etc/sysconfig/{{ hadoop.hdfs.data_node.service.name }}
    - source: salt://hadoop/files/environment
    - template: jinja
    - context:
        environment: {{
          salt.slsutil.merge(
            hadoop.environment, salt.slsutil.merge(
              hadoop.hdfs.environment,
              hadoop.hdfs.data_node.environment
            )
          )
        }}

With slsutil.merge_all:

{{ hadoop.hdfs.data_node.service.name }}_environment_file_installed:
  file.managed:
    - name: /etc/sysconfig/{{ hadoop.hdfs.data_node.service.name }}
    - source: salt://hadoop/files/environment
    - template: jinja
    - context:
        environment: {{
          salt.slsutil.merge_all([
            hadoop.environment,
            hadoop.hdfs.environment,
            hadoop.hdfs.data_node.environment
          ])
        }}

I'm interested to know if you all think it would be better to add this function or to overload the merge function.

What does this PR do?

This PR adds a merge_all function to the slsutil module

What issues does this PR fix or reference?

None

Tests written?

No

Commits signed with GPG?

Yes

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[rallytime]

Can you add some more documentation to this new function? Each arg/kwarg should be documented.

Can you also add a ..versionadded:: Fluorine directive?

[onlyanegg]

Thanks @rallytime, @gtmanfred, @cachedout. I've added the versionadded tag and argument documentation.