Allow packaging shared object files in Python projects

**Description:**

I'm working on a Python project that indirectly uses a native library through `ctypes`, so I need to supply the library, `libspatialindex.so`, in the Lambda function's package. However, when I run `sam build`, the file does not get copied into the output. It looks like this is due to the [EXCLUDED_FILES](https://github.com/awslabs/aws-lambda-builders/blob/6696532b302c3974a6f0c1750ff572e768187cec/aws_lambda_builders/workflows/python_pip/workflow.py#L21) list for `PythonPipWorkflow`.

**Steps to reproduce the issue:**
1. Place a file ending in `.so` in the directory pointed to by `CodeUri`
2. Run `sam build`

**Observed result:**
The file should be copied into `.aws-sam/build/FunctionName/`

**Expected result:**
The file is missing

**Additional environment details (Ex: Windows, Mac, Amazon Linux etc)**
I am using SAM CLI version 0.16.0 on Debian Stretch