Pretrain SSD-MobileNetv1 model

[Matthew Brookhart]

We should be able to reuse https://github.com/apache/incubator-mxnet/tree/master/example/ssd with the mobilenetv1 symbol.

Acceptance Criteria:

1. Train model to the default number of epochs and within 10% expected accuracy (on GPU)
2. Upload saved model symbol json and parameters to deepmark
3. Provide a script for testing model accuracy on test data.

[ruby-nervana]

Made the following changes to run SSD example with MobileNetV2 symbol (MXNet repo revision c792c9f). Am currently training the model on Pascal VOC.

1. Moved example/image-classification/symbols/mobilenetv2.py to example/ssd/symbol
2. Added the following code to example/ssd/symbol/symbol_factory.py get_config function if statement:

elif network == 'mobilenetv2':
        num_layers = 1 + 17*3 + 2  # conv layers
        network = 'mobilenetv2'
        from_layers = ['seq-5-block1-exp-relu6', 'last-1x1-conv-relu6', '', '', '', '']
        num_filters = [-1, -1, 512, 256, 256, 128]
        strides = [-1, -1, 2, 2, 2, 2]
        pads = [-1, -1, 1, 1, 1, 1]
        sizes = [[.1, .141], [.2,.272], [.37, .447], [.54, .619], [.71, .79], [.88, .961]]
        ratios = [[1,2,.5], [1,2,.5,3,1./3], [1,2,.5,3,1./3], [1,2,.5,3,1./3], \
            [1,2,.5], [1,2,.5]]
        normalizations = -1
        steps = []
        return locals()

3. In ssd/train/train_net.py line 222 hack: changed elif pretained to elif False
4. In ssd/config/config.py line 19: changed from config.utils import to from utils import
5. add **kwargs to get_symbol function in mobilenetv2.py

Then from ssd folder run
python train.py --train-path <path to created train.rec> --val-path <path to created val.rec> --network mobilenetv2 --prefix <path to model save dir>/ssd

Where train.rec and val.rec were created for Pascal VOC following the README

[ruby-nervana]

I just realized this ticket requests MobileNet v1, not v2. Will change accordingly.

[ruby-nervana]

Model files, data, test script and README have been saved to /nfs/fm/disks/aipg_trained_models_01/mxnet/ssd-mobilenet-v1