Improve end-to-end test output

.travis.yml

@@ -14,4 +14,4 @@ script:
   - go vet
   - go test -v ./...
   - go build
-  - ./end-to-end-test.sh -v
+  - ./end-to-end-test.sh

end-to-end-test.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 
-set +euf +o pipefail
+set -euf +o pipefail
 
 cd "$(dirname $0)"
 
@@ -33,6 +33,11 @@ do
   esac
 done
 
+if [ ! -x ./node_exporter ]
+then
+    echo './node_exporter not found. Consider running `go build` first.' >&2
+    exit 1
+fi
 
 ./node_exporter \
   -collector.procfs="collector/fixtures/proc" \
@@ -62,6 +67,7 @@ finish() {
   then
     kill -9 "$(cat ${tmpdir}/node_exporter.pid)"
     # This silences the "Killed" message
+    set +e
     wait "$(cat ${tmpdir}/node_exporter.pid)" > /dev/null 2>&1
     rm -rf "${tmpdir}"
   fi