[v2.0] Add Optim Warning

[barry-jin]

Description

Optimizers in MXNet2.0 are refactored and some have new keyword name for the parameters, like adagrad(eps->epsilon), rmsprop(gamma1->rho, gamma2->momentum). It will be confusing for users who migrate from v1.x to find that using rmsprop could raise the following error:

Traceback (most recent call last):
  File "optimizer_update.py", line 16, in <module>
    rmsprop_optimizer = optimizer.RMSProp(learning_rate=0.001, gamma1=0.9, gamma2=0.9, epsilon=1e-07, centered=False)
  File "/home/ubuntu/workspace/incubator-mxnet/python/mxnet/optimizer/rmsprop.py", line 73, in __init__
    super(RMSProp, self).__init__(learning_rate=learning_rate,
  File "/home/ubuntu/workspace/incubator-mxnet/python/mxnet/optimizer/optimizer.py", line 96, in __init__
    super(Optimizer, self).__init__(**kwargs)
TypeError: object.__init__() takes exactly one argument (the instance to initialize)

This PR will add warnings for deprecated parameters in the following optimizers:

1. adagrad:
   • eps -> epsilon
2. rmsprop:
   • gamma1 -> rho
   • gamma2 -> momentum

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

Comments

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

[mxnet-bot]

Hey @barry-jin , Thanks for submitting the PR
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[barry-jin]

@mxnet-bot run ci [centos-gpu]

[mxnet-bot]

Jenkins CI successfully triggered : [centos-gpu]

[barry-jin]

@mxnet-bot run ci [centos-gpu]

[mxnet-bot]

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