vcl: move child wrk cleanup from sighandler to vls_epoll_wait
vcl: move child wrk cleanup from sighandler to vls_epoll_wait

Main process may enter sighandler with a lock, such as lock in localtime
or in mspace_free, and child wrk cleanup may try to get such locks and
cause deadlock.
The patch move cleanup to vls_epoll_wait to wait app's next call.

Type: fix

Signed-off-by: wanghanlin <2a7ca241eb4a7ff06d4307cab23ef63455935ec6@corp.netease.com>
Change-Id: I9b208038a0f49b0ace44684189234aeac9d94730

chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp