unstable tests in server and privilege/privileges

[morgo]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

make gotest

2. What did you expect to see? (Required)

pass

3. What did you see instead (Required)

Failed tests:

--- FAIL: TestUptime (0.07s)
    stat_test.go:56: 
                Error Trace:    stat_test.go:56
                Error:          Received unexpected error:
                                listen tcp 127.0.0.1:4000: bind: address already in use
                                github.com/pingcap/errors.AddStack
                                        /home/morgo/go/pkg/mod/github.com/pingcap/[email protected]/errors.go:174
                                github.com/pingcap/errors.Trace
                                        /home/morgo/go/pkg/mod/github.com/pingcap/[email protected]/juju_adaptor.go:15
                                github.com/pingcap/tidb/server.NewServer
                                        /home/morgo/go/src/github.com/morgo/tidb/server/server.go:243
                                github.com/pingcap/tidb/server.TestUptime
                                        /home/morgo/go/src/github.com/morgo/tidb/server/stat_test.go:55
                                testing.tRunner
                                        /usr/local/go/src/testing/testing.go:1439
                                runtime.goexit
                                        /usr/local/go/src/runtime/asm_amd64.s:1571
                Test:           TestUptime
FAIL
coverage: 67.1% of statements

coverage: 84.1% of statements
goleak: Errors on successful test run: found unexpected goroutines:
[Goroutine 39136 in state IO wait, with internal/poll.runtime_pollWait on top of the stack:
goroutine 39136 [IO wait]:
internal/poll.runtime_pollWait(0x7f3ff5f629b8, 0x72)
        /usr/local/go/src/runtime/netpoll.go:302 +0x89
internal/poll.(*pollDesc).wait(0xc002729480?, 0xc0014dd000?, 0x0)
        /usr/local/go/src/internal/poll/fd_poll_runtime.go:83 +0x32
internal/poll.(*pollDesc).waitRead(...)
        /usr/local/go/src/internal/poll/fd_poll_runtime.go:88
internal/poll.(*FD).Read(0xc002729480, {0xc0014dd000, 0x1000, 0x1000})
        /usr/local/go/src/internal/poll/fd_unix.go:167 +0x25a
net.(*netFD).Read(0xc002729480, {0xc0014dd000?, 0x123e7c9?, 0x4?})
        /usr/local/go/src/net/fd_posix.go:55 +0x29
net.(*conn).Read(0xc0056e7848, {0xc0014dd000?, 0xc0056e7840?, 0x1?})
        /usr/local/go/src/net/net.go:183 +0x45
net/http.(*persistConn).Read(0xc0028a9200, {0xc0014dd000?, 0xc001bfe840?, 0xc0000afd30?})
        /usr/local/go/src/net/http/transport.go:1929 +0x4e
bufio.(*Reader).fill(0xc00117a1e0)
        /usr/local/go/src/bufio/bufio.go:106 +0x103
bufio.(*Reader).Peek(0xc00117a1e0, 0x1)
        /usr/local/go/src/bufio/bufio.go:144 +0x5d
net/http.(*persistConn).readLoop(0xc0028a9200)
        /usr/local/go/src/net/http/transport.go:2093 +0x1ac
created by net/http.(*Transport).dialConn
        /usr/local/go/src/net/http/transport.go:1750 +0x173e

 Goroutine 39137 in state select, with net/http.(*persistConn).writeLoop on top of the stack:
goroutine 39137 [select]:
net/http.(*persistConn).writeLoop(0xc0028a9200)
        /usr/local/go/src/net/http/transport.go:2392 +0xf5
created by net/http.(*Transport).dialConn
        /usr/local/go/src/net/http/transport.go:1751 +0x1791
]
FAIL    github.com/pingcap/tidb/privilege/privileges    12.261s

### 4. What is your TiDB version? (Required)

master