fix test

[baurine]

• 1 second to load server info is too short, always fails
• although 2 seconds can make test pass, prefer to increase larger

error logs when fails:

> make
Running in native mode.

----------------------------------------------------------------------
FAIL: service_test.go:63: serviceSuite.TestRPCServerInfo

service_test.go:77:
    c.Assert(err, IsNil)
... value *status.statusError = &status.statusError{Code:4, Message:"context deadline exceeded", Details:[]*any.Any(nil), XXX_NoUnkeyedLiteral:struct {}{}, XXX_unrecognized:[]uint8(nil), XXX_sizecache:0} ("rpc error: code = DeadlineExceeded desc = context deadline exceeded")

OOPS: 4 passed, 1 FAILED
--- FAIL: TestT (1.04s)
FAIL
coverage: 56.1% of statements
FAIL    github.com/pingcap/sysutil      3.373s
FAIL
make: *** [gotest] Error 1

[baurine]

@crazycs520 @lonng PTAL, thanks!

[crazycs520]

LGTM