Test multiple scripts in one task executing with different UIDs

Prior to this commit we weren't testing whether scripts were executable
when UIDs differed from Step to Step in a single Task.

This commit updates the step-script examples to vary the UID of each
Step. A failure of one of these would indicate that a bug has
been introduced in the permissions of the shell scripts that Tekton
generates and places in the /tekton/scripts directory.

examples/v1alpha1/taskruns/step-script.yaml

@@ -18,6 +18,11 @@ spec:
       env:
       - name: FOO
         value: foooooooo
+      # Test that Pods with containers run as different UIDs
+      # are able to run scripts regardless of any specific
+      # Step's UID.
+      securityContext:
+        runAsUser: 2000
       script: |
         #!/usr/bin/env bash
         set -euxo pipefail
@@ -30,6 +35,8 @@ spec:
 
     - name: place-file
       image: ubuntu
+      securityContext:
+        runAsUser: 8000
       script: |
         #!/usr/bin/env bash
         echo "echo Hello from script file" > /workspace/hello
@@ -42,6 +49,8 @@ spec:
 
     - name: contains-eof
       image: ubuntu
+      securityContext:
+        runAsUser: 16000
       script: |
         #!/usr/bin/env bash
         cat > file << EOF

examples/v1beta1/taskruns/step-script.yaml

@@ -17,6 +17,11 @@ spec:
       env:
       - name: FOO
         value: foooooooo
+      # Test that Pods with containers run as different UIDs
+      # are able to run scripts regardless of any specific
+      # Step's UID.
+      securityContext:
+        runAsUser: 2000
       script: |
         #!/usr/bin/env bash
         set -euxo pipefail
@@ -29,6 +34,8 @@ spec:
 
     - name: place-file
       image: ubuntu
+      securityContext:
+        runAsUser: 8000
       script: |
         #!/usr/bin/env bash
         echo "echo Hello from script file" > /workspace/hello
@@ -41,6 +48,8 @@ spec:
 
     - name: contains-eof
       image: ubuntu
+      securityContext:
+        runAsUser: 16000
       script: |
         #!/usr/bin/env bash
         cat > file << EOF