Fix coverage-bin script

Signed-off-by: Joffrey F <joffrey@docker.com>

Author: shin-

e2e/coverage-bin

@@ -1,11 +1,15 @@
-#!/bin/sh
+#!/bin/bash
 
 # This script is a proxy that injects the required test flags and strips out test output
 # It allows us to use a coverage-enabled binary for e2e tests
 
-../_build/docker-app.cov \
-    -test.coverprofile=../_build/cov/$(uuidgen).out \
-    $* \
+BUILD_DIR=${BASH_SOURCE%/*}/../_build
+
+$BUILD_DIR/docker-app.cov \
+    -test.coverprofile=$BUILD_DIR/cov/$(uuidgen).out \
+    "$@" \
 | grep -vE '^PASS$' \
 | grep -vE '^coverage: [0-9]+\.[0-9]+% of statements in .+$' \
 | grep -v '^=== RUN   TestRunMain$'
+
+exit ${PIPESTATUS[0]}