SymbolBlock.imports ignore_extra & allow_missing

[samskalicky]

Description

Allow ignore_extra and allow_missing to be specified in SymbolBlock.imports for loading params.

Allows users to actually act on the error message:

Traceback (most recent call last):
  File "/home/ubuntu/runtime.py", line 258, in __init__
    self._model = mx.gluon.nn.SymbolBlock.imports(local_json_file_path, [self.input_name], local_params_file_path, ctx=self.ctx)
  File "/usr/local/lib/python3.6/dist-packages/mxnet/gluon/block.py", line 1365, in imports
    ret.collect_params().load(param_file, ctx=ctx, cast_dtype=True, dtype_source='saved')
  File "/usr/local/lib/python3.6/dist-packages/mxnet/gluon/parameter.py", line 1020, in load
    ignore_extra, restore_prefix, filename, cast_dtype, dtype_source)
  File "/usr/local/lib/python3.6/dist-packages/mxnet/gluon/parameter.py", line 1066, in load_dict
    name[lprefix:], error_str, _brief_print_list(self._params.keys()))
AssertionError: Parameter 'data' loaded from file:gluon_cv_imagenet_classifier/ResNet18_v1/TVM/compiled-0000.params is not present in ParameterDict, choices are: 'resnetv10_conv0_weight', 'resnetv10_batchnorm0_gamma', 'resnetv10_batchnorm0_beta', ..., 'resnetv10_stage4_batchnorm3_running_mean', 'resnetv10_stage4_batchnorm3_running_var', 'resnetv10_stage4_batchnorm4_running_mean', 'resnetv10_stage4_batchnorm4_running_var'. Set ignore_extra to True to ignore. Please make sure source and target networks have the same prefix.For more info on naming, please see https://mxnet.io/api/python/docs/tutorials/packages/gluon/blocks/naming.html

Checklist

Essentials

• PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage
• Code is well-documented

Changes

• Feature1, tests, (and when applicable, API doc)
• Feature2, tests, (and when applicable, API doc)

Comments

• If this change is a backward incompatible change, why must this change be made.
• Interesting edge cases to note here

[mxnet-bot]

Hey @samskalicky , Thanks for submitting the PR
All tests are already queued to run once. If tests fail, you can trigger one or more tests again with the following commands:

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[samskalicky]

@mxnet-bot run ci [all]

[leezu]

You're inadvertently reverting several other recent PRs here. Please only change the intended lines