Update travis to use go 1.10.x for fixing CI

To fix "go get -u github.com/golang/lint/golint" error.
golang/lint#421

Also fix integratinon test when using golang 1.10.x
In AddProcessToContainer(), the returned stdout buffer has x00 padded, after it is converted to string, it still has padded zeros.
This commit trims the padded zeros in string.

Replace "github.com/golang/lint/golint" with "golang.org/x/lint/golint" from below error message:
(this is needed for golang 1.12 or later)
```
package github.com/golang/lint/golint: code in directory /home/travis/gopath/src/github.com/golang/lint/golint expects import "golang.org/x/lint/golint"
```

Signed-off-by: Xinfeng Liu <[email protected]>

Author: xinfengliu

.travis.yml

@@ -4,8 +4,7 @@ sudo: required
 language: go
 
 go:
-  - 1.8.x
-  - tip
+  - 1.10.x
 
 go_import_path: github.com/containerd/containerd
 
@@ -23,7 +22,7 @@ env:
 install:
   - hack/install-seccomp.sh
   - hack/install-runc.sh
-  - go get -u github.com/golang/lint/golint
+  - go get -u golang.org/x/lint/golint
 
 script:
   - make all

integration-test/exec_test.go

@@ -4,6 +4,7 @@ package main
 
 import (
 	"path/filepath"
+	"strings"
 	"syscall"
 	"time"
 
@@ -58,7 +59,7 @@ func (cs *ContainerdSuite) TestBusyboxTopExecEcho(t *check.C) {
 		t.Assert(*e, checker.Equals, evt)
 	}
 
-	t.Assert(echop.io.stdoutBuffer.String(), checker.Equals, "Ay Caramba!")
+	t.Assert(strings.TrimRight(echop.io.stdoutBuffer.String(), string('\x00')), checker.Equals, "Ay Caramba!")
 }
 
 func (cs *ContainerdSuite) TestBusyboxTopExecTop(t *check.C) {

integration-test/start_linux_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strings"
 	"syscall"
 	"time"
 
@@ -439,7 +440,7 @@ func (cs *ContainerdSuite) TestRestart(t *check.C) {
 
 		t.Assert(*e, checker.Equals, evt)
 	}
-	t.Assert(echop.io.stdoutBuffer.String(), checker.Equals, "Success!")
+	t.Assert(strings.TrimRight(echop.io.stdoutBuffer.String(), string('\x00')), checker.Equals, "Success!")
 
 	// Now kill daemon (SIGKILL)
 	cs.StopDaemon(true)