Feature/#9

[ozbillwang]

• install both aws cli v1 and v2 in same image
• set ENTRYPOINT to switch default aws cli version when run the container.
• if environment variable awscli is set to v2, default aws cli version is v2
• if environment variable awscli is set to v1, not set or set to anything else, except v2, aws cli will be run from /usr/bin, and version is v1
• you can still run specific version with full path in container.
  aws cli v1 - installed at /usr/bin, run as /usr/bin/aws
  aws cli v2 - installed at /usr/local/bin, run as /usr/local/bin/aws
• close Add AWS CLI v2 #9
• since aws cli v2 need glibc, image size increased for about 200MB.

Run a manual test:

$ docker build -t k8s .
$ docker run -ti --rm -e awscli=v2 k8s aws --version
aws-cli/2.1.22 Python/3.7.3 Linux/4.19.121-linuxkit exe/x86_64.alpine.3 prompt/off
$ docker run -ti --rm -e awscli=v1 k8s aws --version
aws-cli/1.18.223 Python/3.8.7 Linux/4.19.121-linuxkit botocore/1.19.63
$ docker run -ti --rm k8s --version
aws-cli/1.18.223 Python/3.8.7 Linux/4.19.121-linuxkit botocore/1.19.63