Fix bug when using tailscale config by file #348

Job	Run time
build / Build	7m 23s
Docker Tests (basics)	1m 11s
E2E Tests (startup)	8m 38s
Docker Tests (bootstraptoken)	57s
Docker Tests (cacerts)	1m 0s
E2E Tests (s3)	5m 49s
E2E Tests (btrfs)	4m 32s
Docker Tests (lazypull)	1m 1s
E2E Tests (externalip)	5m 11s
Docker Tests (upgrade)	34s
E2E Tests (privateregistry)	6m 12s
E2E Tests (wasm)	4m 49s
	47m 17s

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