run golangci-lint in all directories with go.mod (open-telemetry#138)

* Run golangci-lint in all directories with go.mod

* Imports fix by golangci-lint

* Propagate failures from commands running in loops

Makefile

@@ -32,9 +32,13 @@ $(TOOLS_DIR)/stringer: go.mod go.sum tools.go
 
 precommit: $(TOOLS_DIR)/golangci-lint  $(TOOLS_DIR)/misspell $(TOOLS_DIR)/stringer
 	PATH="$(abspath $(TOOLS_DIR)):$${PATH}" go generate ./...
-	$(TOOLS_DIR)/golangci-lint run --fix # TODO: Fix this on windows.
+	# TODO: Fix this on windows.
+	set -e; for dir in $(ALL_GO_MOD_DIRS); do \
+	  echo "golangci-lint in $${dir}"; \
+	  (cd "$${dir}" && $(abspath $(TOOLS_DIR))/golangci-lint run --fix); \
+	done
 	$(TOOLS_DIR)/misspell -w $(ALL_DOCS)
-	for dir in $(ALL_GO_MOD_DIRS); do \
+	set -e; for dir in $(ALL_GO_MOD_DIRS); do \
 	  echo "go mod tidy in $${dir}"; \
 	  (cd "$${dir}" && go mod tidy); \
 	done
@@ -67,7 +71,7 @@ test-386:
 
 .PHONY: examples
 examples:
-	@for ex in $(EXAMPLES); do \
+	@set -e; for ex in $(EXAMPLES); do \
 	  echo "Building $${ex}"; \
 	  (cd "$${ex}" && go build .); \
 	done

example/http/client/client.go

@@ -17,7 +17,6 @@ package main
 import (
 	"context"
 	"fmt"
-	"go.opentelemetry.io/plugin/httptrace"
 	"io/ioutil"
 	"net/http"
 
@@ -26,6 +25,7 @@ import (
 	"go.opentelemetry.io/api/key"
 	"go.opentelemetry.io/api/tag"
 	"go.opentelemetry.io/api/trace"
+	"go.opentelemetry.io/plugin/httptrace"
 )
 
 var (