How to deal with bad rule of remap.config when reloading?

[Conan <co...@gmail.com>]

Hi,

Currently(3.0.1), traffic_server will exit if exists bad rules in
remap.config, whenever startup or reload ( traffic_line -x ).

Bad rules I found:
1. duplicate map rule ( ATS 2.x will use first one and ignore the left ).
2. add a remap plugin which is not exist.
3. return TS_ERROR in TSRemapNewInstance ( eg. check pparam's format.  Now I
always return TS_SUCCESS to prevent the "crash" )

Especially in a "cluster" setup (reverse proxy), remap.config may change
frequently. If remap.config is not edited correctly, whole cluster will
crash when reloading ( not cool ).

I think it's better to pre-check the remap table and not switch to the new
table if remap.config is not enough correct.