Rootcanal catch SIGPIPE

In case the client socket is closed, and rootcanal doesn't detect it due
to TimerTick not fired, writing to the socket causes a SIGPIPE and we
need to catch it to prevent rootcanal from crash.

Bug: 138259663
Test: run_cert.sh with empty test case
Change-Id: I3b9753cfc1cf09fcd7ea123d79048a9b8bacdd87