[Bash] Bash generator improvements

[bkryza]

PR checklist

• Read the contribution guildelines.
• Ran the shell/batch script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates)
• Filed the PR against the correct branch: master for non-breaking changes and 2.3.0 branch for breaking (non-backward compatible) changes.

Description of the PR

@wing328

I've made some improvements to the Bash codegen generator, mostly minor:

• Made Bash autocomplete scripts compatible with bash-completion earlier than 1.4
• Improved Bash autocompletion of operation arguments
• Improved Zsh autocompletion of operation arguments (no extra space added)
• Added mime type abbreviation completion for Zsh autocompletion
• Added generation of Dockerfile which builds a preconfigured image with autocompletion for Zsh and Bash out of the box

You can check out the generated Dockerfile in few simple steps:

mvn package

java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate -i http://petstore.swagger.io/v2/swagger.json -l bash -o generated/bash/petstore -c modules/swagger-codegen/src/test/resources/2_0/bash-config.json

cd generated/bash/petstore

docker build -t petstore-cli .

docker run -it petstore-cli

[Swagger Petstore] $ export PETSTORE_HOST=http://petstore.swagger.io
[Swagger Petstore] $ pet[TAB]
[Swagger Petstore] $ petstore-cli -h
[Swagger Petstore] $ petstore-cli fi[TAB]
[Swagger Petstore] $ petstore-cli findPetById -h
[Swagger Petstore] $ petstore-cli findPetById [TAB]
[Swagger Petstore] $ petstore-cli findPetsByStatus status=available

[wing328]

@bkryza the enhancement looks good to me. Thanks for the PR.