Load pretrained weights when multiple models exist

[taehoonlee]

When multiple models exist, pretrained() from the second doesn't work.

import tensorflow as tf
import tensornets as nets

inputs = tf.placeholder(tf.float32, [None, 224, 224, 3])
model1 = nets.ResNet50(inputs, scope='abc')
model2 = nets.Inception2(inputs, scope='def')
model3 = nets.DenseNet121(inputs, scope='ghi')

with tf.Session() as sess:
    sess.run(model1.pretrained())  # O
    try:
        sess.run(model2.pretrained())  # X
    except:
        print('X')
    try:
        sess.run(model3.pretrained())  # X
    except:
        print('X')