As a Machine I get the created Test Execution Keys from the response JSON

As a Machine I get the created Test Execution Keys from the response JSON.
Currently these are being sent to log file but it requires to search the all log.

Each post task, at the end should create/update 3 build variables:

1. XRAY_RAW_RESPONSE - the String with the raw response from the endpoint. If more than one request were made, all the responses will be joined by ';'.
2. XRAY_TEST_EXECS - the list of Test Executions Updated/Created (if available). If more than one issue was modified, all keys will be joined by ';'.
3. XRAY_TESTS - the list of Test Updated/Created (if available). If more than one issue was modified, all keys will be joined by ';'.
4. XRAY_ISSUES_MODIFIED - list of all issues modified/created. If more than one issue was modified, all keys will be joined by ';'.
5. XRAY_IS_REQUEST_SUCCESSFUL - 'true' if all requests were successful, 'false' otherwise.

By default, these variables have an empty string has value.

These variables should only be available within the scope of a build and should not impact any other build environment.

Due to Jenkins limitations, Pipeline projects will not be supported.

Currently, Xray Cloud doesn't send the list of Tests Updated/Created on the response JSON, so the # XRAY_TESTS from Cloud instances will always be empty.