[IO] Add Redis Connector

[gypleon]

Test cases

- Preparation

1. Flush Redis data using "/data/opt/course/redis/flushall-cluster.sh"
2. Check configuration file "$HUSKY_ROOT/test/test-redis-config.ini"

- Test 1: CMake

1. Follow the standard Cmake commands of Husky.
2. make "Master".
3. make "TestRedisOutputFormat".
4. make "TestRedisInputOutputFormat".
5. make "WordCountRedis".

Expectation: running well.
Notes:

- Test 2: enwiki from MongoDB to Redis:

1. Run "./Master -C test-redis-config.ini"
2. Run "time /data/opt/tmp/exec.sh ./TestRedisOutputFormat -C test-redis-config.ini"

Expectation: running well. 4825150 records to be imported. around 1m30s.
Notes: MUST wait for 10 minutes before Test 3, because for the first time data were loaded into Redis cluster, it takes time for master-slave synchronization.

- Test 3: enwiki from Redis to Redis:

1. Run "./Master -C test-redis-config.ini"
2. Run "time /data/opt/tmp/exec.sh ./TestRedisInputOutputFormat -C test-redis-config.ini"

Expectation: running well. 4825150 records to be imported. around 1m.
Notes: On Husky-worker side, "waiting for keys" logs may be printed as expected, which means that some workers are waiting for keys from the next batch.

- Test 4: enwiki WordCount:

1. Run "./Master -C test-redis-config.ini"
2. Run "time /data/opt/tmp/exec.sh ./WordCountRedis -C test-redis-config.ini"

Expectation: running well. 4825150 records to be imported. around 50s.
Notes: Can be performed consecutively without restart Husky-Master.

[gypleon]

OMG!!! I merged these commits for several hours... but they come out again... maybe I made a ridiculous mistake that override the merge operations.... OMG.... actually, "[IO] Add Redis Connector. Fixed merge conflicts." (38ce3c2) is supposed to be the ONLY ONE left.

I am currently searching for safely merging solutions.

[gypleon]

Hi Legend,
I think the commit problem has been fixed. Please review and leave me comments.
Thanks.

[kygx-legend]

This PR is including other commits in master branch which are not merged into experimental branch. Could you redo the rebase?

[gypleon]

No problem.

[kygx-legend]

This branch is updated to master now. Please rebase again!

[kygx-legend]

And you can run ./scripts/clang-format.py -o check to see what does not match the coding style and run ./scripts/clang-format.py -o replace to fix those errors automatically. Then use lint.py to double check.