e2e logger test: handle paths in Kubernetes CI

Source code paths during //test/e2e/framework/log:go_default_test in
the Kubernetes CI start with relative paths. To avoid too broad
matching of the regex, those paths that occur in practice are named
explicitly as alternatives to the leading slash.

Author: pohly

test/e2e/framework/log/logger_test.go

@@ -148,8 +148,9 @@ func stripAddresses(in string) string {
 	return instanceAddr.ReplaceAllString(in, ">")
 }
 
-// stackLocation matches "\t/<some path>/<file>.go:75 +0x1f1".
-var stackLocation = regexp.MustCompile(`/.*/([[:^space:]]+.go:[[:digit:]]+)( \+0x[0-9a-fA-F]+)?`)
+// stackLocation matches "<some path>/<file>.go:75 +0x1f1" after a slash (built
+// locally) or one of a few relative paths (built in the Kubernetes CI).
+var stackLocation = regexp.MustCompile(`(?:/|vendor/|test/|GOROOT/).*/([[:^space:]]+.go:[[:digit:]]+)( \+0x[0-9a-fA-F]+)?`)
 
 // functionArgs matches "<function name>(...)".
 var functionArgs = regexp.MustCompile(`([[:alpha:]]+)\(.*\)`)