`sam build` for Gradle using gradlew does not work with --use-container

[sanathkr]

Description

Briefly describe the bug you are facing.
When a Gradle project uses gradlew scripts, this file does not get picked up with building inside a container.

Steps to reproduce

Provide steps to replicate.
This integration test sets everything up to repro this issue - https://github.com/awslabs/aws-sam-cli/blob/develop/tests/integration/buildcmd/test_build_cmd.py#L256

Observed result

Please provide command output with --debug flag set.
gradle installation within the container is used instead of the gradlew script

Expected result

Describe what you expected.
gradlew script is used to build the project

Additional environment details (Ex: Windows, Mac, Amazon Linux etc)

1. OS:
2. sam --version:

Add --debug flag to command you are running