tapchannel: improve aux signer signal handling #3149

Job	Run time
Docker build check	3m 12s
cross compilation	10m 19s
Format check	29s
Compilation check	55s
run itests	9m 28s
run itests postgres	17m 5s
migration version check	17s
Lint check	2m 52s
go mod check	20s
RPC check	1m 11s
run LiT tests	17m 28s
sample configuration check	36s
Sqlc check	32s
test vector check	50s
run unit tests (unit-race)	6m 44s
run unit tests (unit-cover)	3m 47s
run unit tests (unit dbbackend=postgres)	4m 51s
finish	3s
	1h 20m 59s

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