[New Generator shell] improve gen_name parsing

Created by: karismann

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: master, 3.4.x, 4.0.x. Default: master.

Description of the PR

• fix #1795 (closed) : test path/package name for generated test in case of composed generated name (i.e java-newframework)
• use the camelized generated name everywhere in the generation script (remove blank and underscore)
• add an error if no generator type are in parameter (i.e. ./new.sh -n 'java-greatframework' -t)

here is some test done with the new version of the script :

$ ./new.sh -n 'java-greatframework' -s -t
Creating modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaGreatframeworkServerCodegen.java
Creating modules/openapi-generator/src/main/resources/java-greatframework-server/README.mustache
Creating modules/openapi-generator/src/main/resources/java-greatframework-server/model.mustache
Creating modules/openapi-generator/src/main/resources/java-greatframework-server/api.mustache
Creating bin/windows/java-greatframework-server-petstore.bat
Creating bin/java-greatframework-server-petstore.sh
Creating modules/openapi-generator/src/test/java/org/openapitools/codegen/java/greatframework/JavaGreatframeworkServerCodegenTest.java
Creating modules/openapi-generator/src/test/java/org/openapitools/codegen/java/greatframework/JavaGreatframeworkServerCodegenModelTest.java
Creating modules/openapi-generator/src/test/java/org/openapitools/codegen/java/greatframework/JavaGreatframeworkServerCodegenOptionsTest.java
Creating modules/openapi-generator/src/test/java/org/openapitools/codegen/options/JavaGreatframeworkServerCodegenOptionsProvider.java
Finished.

$ ./new.sh -n 'java greatframework3' -t -c
Creating modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaGreatframework3ClientCodegen.java
Creating modules/openapi-generator/src/main/resources/java-greatframework3-client/README.mustache
Creating modules/openapi-generator/src/main/resources/java-greatframework3-client/model.mustache
Creating modules/openapi-generator/src/main/resources/java-greatframework3-client/api.mustache
Creating bin/windows/java-greatframework3-client-petstore.bat
Creating bin/java-greatframework3-client-petstore.sh
Creating modules/openapi-generator/src/test/java/org/openapitools/codegen/java/greatframework3/JavaGreatframework3ClientCodegenTest.java
Creating modules/openapi-generator/src/test/java/org/openapitools/codegen/java/greatframework3/JavaGreatframework3ClientCodegenModelTest.java
Creating modules/openapi-generator/src/test/java/org/openapitools/codegen/java/greatframework3/JavaGreatframework3ClientCodegenOptionsTest.java
Creating modules/openapi-generator/src/test/java/org/openapitools/codegen/options/JavaGreatframework3ClientCodegenOptionsProvider.java
Finished.

$ ./new.sh -n 'java-greatframework' -t
[error] You may set a generator type