*: add some logs to help debug error. (pingcap#2253) (pingcap#2357)

cmd: add more logs to debug cdc data-dir set up. (pingcap#2334) (ping…

…cap#2363)

cdc: fix server etcd may nil by create a new local client. (pingcap#2161

) (pingcap#2166)

tests: remove --sort-dir in test scripts (pingcap#2110) (pingcap#2120)

* remove --sort-dir in run_cdc_server script.

* remove sort-dir config in all testcase.

* make data-dir conflict .

* add --data-dir flag, to make dir conflict.

* Update tests/unified_sorter_sort_dir_conflict/run.sh

Co-authored-by: Neil Shen <[email protected]>

Co-authored-by: JinlingChristopher <[email protected]>
Co-authored-by: Ling Jin <[email protected]>
Co-authored-by: Neil Shen <[email protected]>

kv/client: add incremental scan region count limit (pingcap#1926)

kv/client: add incremental scan region count limit (pingcap#1926)

kv/client: add incremental scan region count limit (pingcap#1981)

sorter: provide more information on sorter IO errors (pingcap#1969)

etcd_worker: fix a bug that etcd worker maybe lost data at starting (p…

…ingcap#1813)

cmd: hide --sort-dir in changefeed command. (deprecated warning exist…

…s) (pingcap#1784) (pingcap#1794)