Improve matching Keras `kernel_initializer` strings and callables

[HunterMcGushion]

• Experiment matching incorrectly considers a string kernel_initializer value to be different from a callable value for the same function, with the default arguments
• This problem may be encountered if frequently switching between using kernel_initializer strings and callables. Nothing “breaks” as a result of this issue; however, some valid learning material may be ignored
• There are already a number of test cases in place to check this functionality marked “xfail” in tests/smoke_tests/test_keras.py

Note

• This issue (along with several others) was originally opened by @caprone in #111, but it is being moved here for easier tracking
• If this issue is missing any important information from #111, please feel free to mention/paste it