Two stage BE application image support - stage1 base image + stage2 app image

[rameshpolishetti]

Context
Add support to create BE container image in 2 stages.

Stage1 - create base image from local BE installation / from installer zips

build_image -i base
-s <installers-directory/BE_HOME_location>
-t <base-image-name>:<base-image-version>           # base image tag to be created

Stage2 - create application image from the base image created in stage1 + application cdd/ear

build_image -i app
-s <base-image-name>:<base-image-version>
-a <apps-artifact-directory>
-t <app-image-name>:<app-image-version>           # application image tag to be created

Alternatives
you can achieve the same by using s2i option - https://github.com/TIBCOSoftware/be-tools/wiki/Building-TIBCO-BusinessEvents-Application#method-two---building-using-source-to-image-s2i-toolkit
this option requires s2i cli installed

Has the feature been requested before?
Issue - #362

If the feature request is approved, would you be willing to submit a PR?
Yes

[rameshpolishetti]

Adding @vpatil-tibco to review the requirement