KNOX-3297: Docker entrypoint script has issues that prevents this image being run as docker container and as a pod in k8s

[sneethiraj]

(It is very important that you created an Apache Knox JIRA for this change and that the PR title/commit message includes the Apache Knox JIRA ID!)

KNOX-3297: Docker entrypoint script has issues that prevents this image being run as docker container and as a pod in k8s

What changes were proposed in this pull request?

1. Modified to use keytool from the PATH instead of hardcoding it.
2. Fixed a scripting error related to default init of MASTER_S... environment variable.
3. Added additional validation for file existance before additing it to truststore. Also, introduced a custom env variable TRUSTSTORE_IMPORTS to allow customers to add more number of certificates into truststore.

How was this patch tested?

1. Validated the changes as standalone docker [run]
2. Validated by running the docker image as k8s pod

(Please explain how this patch was tested. For instance: running automated unit/integration tests, manual tests. Please write down your test steps as detailed as possible)

Integration Tests

no new integration tests.

UI changes

None.

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[github-actions]

Test Results

16 tests   16 ✅  1s ⏱️
 1 suites   0 💤
 1 files     0 ❌

Results for commit d8569eb.