[DistDGL] sort node/edge_map to obtain expected id ranges

[Rhett-Ying]

Description

under the help of sorting logic added here, any previously partitioned graphs/jsons could be handled correctly.
what's more, sort_keys=False will make sure dumped node/edge_map is what we expected.

Checklist

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [$CATEGORY] (such as [NN], [Model], [Doc], [Feature]])
• I've leverage the tools to beautify the python and c++ code.
• The PR is complete and small, read the Google eng practice (CL equals to PR) to understand more about small PR. In DGL, we consider PRs with less than 200 lines of core code change are small (example, test and documentation could be exempted).
• All changes have test coverage
• Code is well-documented
• To the best of my knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change
• Related issue is referred in this PR
• If the PR is for a new model/paper, I've updated the example index here.

Changes

[dgl-bot]

To trigger regression tests:

• @dgl-bot run [instance-type] [which tests] [compare-with-branch];
  For example: @dgl-bot run g4dn.4xlarge all dmlc/master or @dgl-bot run c5.9xlarge kernel,api dmlc/master

[dgl-bot]

Commit ID: 01752b3

Build ID: 1

Status: ❌ CI test failed in Stage [Distributed Torch CPU Unit test].

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[dgl-bot]

Commit ID: 01752b3

Build ID: 2

Status: ❌ CI test failed in Stage [Distributed Torch CPU Unit test].

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[dgl-bot]

Commit ID: 01752b3

Build ID: 3

Status: ❌ CI test failed in Stage [Distributed Torch CPU Unit test].

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[dgl-bot]

Commit ID: 01752b3

Build ID: 4

Status: ❌ CI test failed in Stage [Distributed Torch CPU Unit test].

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Full logs path: link

[dgl-bot]

Commit ID: 4028d7d456d5727486b1bfbdfd7da0cbe753b70b

Build ID: 5

Status: ❌ CI test failed in Stage [Distributed Torch CPU Unit test].

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[dgl-bot]

Commit ID: 43586e9a441861da1c8053e8cb2ab9dc102cd6b9

Build ID: 6

Status: ✅ CI test succeeded.

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