Redis functionality exporter

This is a simple exporter for Redis that exports the following metrics:

• redis_connection_time (in seconds)
• is_working (1 if the exporter is working, 0 if not) - it uses checkRedisFunctionality() to check is the redis server is working
• redis_write_time (in seconds) - it uses WriteRedis() to check the write time
• redis_read_time (in seconds) - it uses ReadRedis() to check the read time
• redis_delete_time (in seconds) - it uses DeleteRedis() to check the delete time

TODO:

• [] replace fmt.Println and os.Exit with log.Fatal
• [] read configuration from environment variables and if it's not set read it from config.yml file
• [] write deployment
• [] create configmap example
• [] write test
• [] update readme