Variables are not resolved for execution of che commands

[RomanNikitenko]

Describe the bug

We have ability to define variables like ${file} for che commands in a devfile.
It works well for theia tasks, but doesn't work for che commands.

Che version

• latest
• nightly
• other: che-theia:7.0.0-next

Steps to reproduce

1. Use in devfile command like:

- name: copy content
  actions:
  - type: exec
    component: che-dev
    command: >
              cp ${workspaceFolder}/.theia/tasks.json ${workspaceFolder}/cheCommands.json
    workdir: /projects

2. Run the task
3. You can see that task can not be executed because the variable is not resolved

Expected behavior

The variable is resolved and the task is executed

Runtime

• kubernetes (include output of kubectl version)
• Openshift (include output of oc version)
• minikube (v1.0.0)
• minishift (include output of minishift version and oc version)
• docker-desktop + K8S (include output of docker version and kubectl version)
• other: (please specify)

Installation method

• chectl chectl/0.0.2-6d3894f linux-x64 node-v10.4.1
• che-operator
• minishift-addon
• I don't know

Environment

• my computer
  • Windows
  • Linux
  • macOS
• Cloud
  • Amazon
  • Azure
  • GCE
  • other (please specify)
• other: please specify

[RomanNikitenko]

I created the PR for 7.0.0 branch, please let me know if this changes are assumed for 7.0.0.

[slemeur]

P2 but would be nice to include it in 7.0.0 as it will allow to solve the issue from #14007