Avoid Groovy calls that require script approval

[kthoms]

While there is control over script approvals on Xtext JIPP, there isn't in Xtext CJE based Jenkins. And it is unlikely that approval is granted for some Groovy functions.

In general, it should be avoided to do processing with scripts in Jenkinsfiles that might cause trouble with the Groovy Sandbox.

To avoid this there are multiple possibilities:

• execute plan bash commands within Groovy functions. This is already done for multiple manipulations
• executing Groovy via shell command. On CJE there is the possibility to run on docker images. Use docker pull docker.io/smoht/xtext-buildenv:latest. Everything that is valid there can be done.
• Use a Jar from somewhere with CLI programs