Find an elegant solution to rotate Gatekeeper's log file

[mengxiang0811]

In #139 using an lcore just for a timer is quite wasteful. For now, we are going to add this burden on the LLS block. This issue is meant to find an elegant solution to redirect DPDK log to file without mixing the code with the LLS block, or wasting an lcore.

[AltraMayor]

Perhaps, a viable solution is to have a multiplexer block that multiplexes an lcore with lightweight blocks such as the following blocks: LLS, log rotation, CPS, and dynamic configuration. In order to have a non-preemptive multiplexer block, which is much simpler to implement, one would need to rewrite each lightweight block that can be multiplexed to not block at each call. That is, the multiplexer block would work as an event library that the lightweight blocks would use to register their handlers. Not only would this solution solve the log rotation problem, but it would also take away two lcores from Gatekeeper and Grantor servers that today are used for lightweight blocks.

[AltraMayor]

Instead of using an event model for the multiplexed blocks, it'd be easier to use coroutines. Thus, most of the current code would not need to change and the complexity of the code would not increase that much.