Don't assume $0 is the script source

Part of our 'downstream' CI we reuse the `test/e2e-common.sh` functions, we have
a script that source the test/e2e-common.sh and run with the downstream
specifics functions.

$0 in the e2e-common assume the script is run from `test/e2e-tests.sh` when our
script which source test/e2e-tests.sh is something else somewhere else.

Let's use git to safely detect the toplevel of the directory

Signed-off-by: Chmouel Boudjnah <chmouel@redhat.com>

Author: chmouel

test/e2e-common.sh

@@ -16,7 +16,7 @@
 
 # Helper functions for E2E tests.
 
-source $(dirname $0)/../vendor/github.com/tektoncd/plumbing/scripts/e2e-tests.sh
+source $(git rev-parse --show-toplevel)/vendor/github.com/tektoncd/plumbing/scripts/e2e-tests.sh
 
 function teardown() {
     subheader "Tearing down Tekton Pipelines"

test/e2e-tests.sh

@@ -17,7 +17,7 @@
 # This script calls out to scripts in tektoncd/plumbing to setup a cluster
 # and deploy Tekton Pipelines to it for running integration tests.
 
-source $(dirname $0)/e2e-common.sh
+source $(git rev-parse --show-toplevel)/test/e2e-common.sh
 
 # Script entry point.
 

test/presubmit-tests.sh

@@ -26,7 +26,7 @@
 export DISABLE_MD_LINTING=1
 export DISABLE_MD_LINK_CHECK=1
 
-source $(dirname $0)/../vendor/github.com/tektoncd/plumbing/scripts/presubmit-tests.sh
+source $(git rev-parse --show-toplevel)/vendor/github.com/tektoncd/plumbing/scripts/presubmit-tests.sh
 
 function post_build_tests() {
   header "running golangci-lint"