SELinux prevents volume mount on Fedora

### Description:

Rather than reopening #676, I'm opening a new issue for the most recent version of aws-sam-cli and docker. Issue #676 was prematurely closed in my opinion with the explanation that the user wasn't using the "current version of sam cli".

On Fedora 32, `sam local invoke` fails to mount a volume due to the fact that selinux prevents access to the host directory from within the docker container unless the `:z` or `:Z` mount option is added to add the [selinux label to the directory](https://docs.docker.com/storage/bind-mounts/#configure-the-selinux-label).

If I run the following `sam local invoke` command using SAM to locally execute the Lambda function in my test repository [here](https://gitlab.com/mbacchi/lambda-env-vars) which uses a volume mount I get the error `[ERROR] Runtime.ImportModuleError: Unable to import module 'app': No module named 'app'`:

```
sam local invoke LambdaEnvVarsFunction --event events/event.json
Invoking app.lambda_handler (python3.7)
Skip pulling image and use local one: amazon/aws-sam-cli-emulation-image-python3.7:rapid-1.7.0.

Mounting /home/user/lambda-env-vars/.aws-sam/build/LambdaEnvVarsFunction as /var/task:ro,delegated inside runtime container
START RequestId: afdda989-cb02-1c82-2916-f3e9927bce7d Version: $LATEST
[ERROR] Runtime.ImportModuleError: Unable to import module 'app': No module named 'app'
END RequestId: afdda989-cb02-1c82-2916-f3e9927bce7d
REPORT RequestId: afdda989-cb02-1c82-2916-f3e9927bce7d Init Duration: 78.38 ms Duration: 2.04 ms Billed Duration: 100 ms Memory Size: 128 MB Max Memory Used: 23 MB

{"errorType":"Runtime.ImportModuleError","errorMessage":"Unable to import module 'app': No module named 'app'"}
```

As discussed in #676, if I try to run Docker without the `:z` mount option I cannot read the contents of the directory:

```
docker run --rm -it -v /home/user/lambda-env-vars/.aws-sam/build/LambdaEnvVarsFunction:/var/task amazon/aws-sam-cli-emulation-image-python3.7 /bin/bash
bash-4.2# ls
ls: cannot open directory .: Permission denied
bash-4.2# exit
```

But it can be verified that the mount works by running Docker with the `:z` option. If I run the following command I am able to see the contents of the mounted volume within the docker container:

```
docker run --rm -it -v /home/user/lambda-env-vars/.aws-sam/build/LambdaEnvVarsFunction:/var/task:z amazon/aws-sam-cli-emulation-image-python3.7 /bin/bash
bash-4.2# ls
__init__.py app.py certifi certifi-2020.6.20.dist-info chardet chardet-3.0.4.dist-info idna idna-2.10.dist-info requests requests-2.24.0.dist-info requirements.txt urllib3 urllib3-1.25.11.dist-info
bash-4.2# pwd
/var/task
bash-4.2# exit

```

Finally, if I use the command also discussed in #676, to change the label on the directory, it allows me to run the `sam local invoke` command:

```
chcon -Rt svirt_sandbox_file_t .aws-sam/

sam local invoke LambdaEnvVarsFunction --event events/event.json
Invoking app.lambda_handler (python3.8)
Skip pulling image and use local one: amazon/aws-sam-cli-emulation-image-python3.8:rapid-1.7.0.

Mounting /home/user/lambda-env-vars/.aws-sam/build/LambdaEnvVarsFunction as /var/task:ro,delegated inside runtime container
START RequestId: a7f74c73-f625-1c23-9fd3-6ffa7ac22051 Version: $LATEST
END RequestId: a7f74c73-f625-1c23-9fd3-6ffa7ac22051
REPORT RequestId: a7f74c73-f625-1c23-9fd3-6ffa7ac22051 Init Duration: 82.44 ms Duration: 1.98 ms Billed Duration: 100 ms Memory Size: 128 MB Max Memory Used: 24 MB

{"statusCode":200,"body":"{\"_HANDLER\": \"app.lambda_handler\", \"AWS_REGION\": \"us-east-1\", \"AWS_EXECUTION_ENV\": \"AWS_Lambda_python3.8\", \"AWS_LAMBDA_FUNCTION_NAME\": \"test\", \"AWS_LAMBDA_FUNCTION_MEMORY_SIZE\": \"128\", \"AWS_LAMBDA_FUNCTION_VERSION\": \"$LATEST\", \"AWS_LAMBDA_LOG_GROUP_NAME\": \"/aws/lambda/test\", \"AWS_LAMBDA_LOG_STREAM_NAME\": \"2020/11/07/[$LATEST]aa421238fa611d2b3e8d42595b803ea9\", \"LANG\": null, \"TZ\": null, \"LAMBDA_TASK_ROOT\": \"/var/task\", \"LAMBDA_RUNTIME_DIR\": \"/var/runtime\", \"PATH\": \"/var/lang/bin:/usr/local/bin:/usr/bin/:/bin:/opt/bin\", \"LD_LIBRARY_PATH\": \"/var/lang/lib:/lib64:/usr/lib64:/var/runtime:/var/runtime/lib:/var/task:/var/task/lib:/opt/lib\", \"PYTHONPATH\": \"/var/runtime\", \"AWS_LAMBDA_RUNTIME_API\": null}"}
```

This appears to still be an open issue with aws-sam-cli related to the most recent version. It should be addressed by mounting with the `:z` or `:Z` mount option on Fedora or other Linuxes using SELinux.

### Steps to reproduce:

1. Clone repo https://gitlab.com/mbacchi/lambda-env-vars ( or use any other SAM template with a volume mount) on Fedora 32.
2. run `sam build`
3. run `sam local invoke LambdaEnvVarsFunction --event events/event.json`

### Observed result:

The volume mount is prevented by SELinux and the error `[ERROR] Runtime.ImportModuleError: Unable to import module 'app': No module named 'app'` is received.

### Expected result:

The volume is mounted in the docker container and the `sam local invoke` command succeeds.

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

1. OS: Fedora 32
2. `sam --version`: `SAM CLI, version 1.7.0`
3. aws cli version: `aws-cli/1.18.118 Python/3.8.6 Linux/5.8.16-200.fc32.x86_64 botocore/1.17.63`
4. docker version: `Docker version 19.03.11, build 42e35e6`

`Add --debug flag to command you are running`

```
sam --debug local invoke LambdaEnvVarsFunction --event events/event.json
Invoking app.lambda_handler (python3.8)
Skip pulling image and use local one: amazon/aws-sam-cli-emulation-image-python3.8:rapid-1.7.0.

Mounting /home/user/lambda-env-vars/.aws-sam/build/LambdaEnvVarsFunction as /var/task:ro,delegated inside runtime container
START RequestId: 00ba8c1a-ee02-1628-1902-e33d6f0e0736 Version: $LATEST
[ERROR] Runtime.ImportModuleError: Unable to import module 'app': No module named 'app'
END RequestId: 00ba8c1a-ee02-1628-1902-e33d6f0e0736
REPORT RequestId: 00ba8c1a-ee02-1628-1902-e33d6f0e0736 Init Duration: 82.01 ms Duration: 2.25 ms Billed Duration: 100 ms Memory Size: 128 MB Max Memory Used: 24 MB

{"errorType":"Runtime.ImportModuleError","errorMessage":"Unable to import module 'app': No module named 'app'"}
```