Fix substitution of NR_NODE_PATH

[HiroyasuNishiyama]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

Substituting environment variable $ {NR_NODE_PATH} does not work properly.
This is because the environment variable replacement is performed before setting _path attribute of the node.
This PR try to fix the issue.

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the forum/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality

[coveralls]

Coverage remained the same at 67.311% when pulling 0f1aea3 on node-red-hitachi:fix-path-substitution into bffb91f on node-red:master.