ipn/{conffile,ipnlocal}: start booting tailscaled from a config file w/ auth key

Updates #1412

Change-Id: Icd880035a31df59797b8379f4af19da5c4c453e2
Co-authored-by: Maisem Ali <maisem@tailscale.com>
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tstest/tstest.go

@@ -16,6 +16,7 @@ import (
 	"tailscale.com/envknob"
 	"tailscale.com/logtail/backoff"
 	"tailscale.com/types/logger"
+	"tailscale.com/util/cibuild"
 )
 
 // Replace replaces the value of target with val.
@@ -76,6 +77,14 @@ func Shard(t testing.TB) {
 	}
 }
 
+// SkipOnUnshardedCI skips t if we're in CI and the TS_TEST_SHARD
+// environment variable isn't set.
+func SkipOnUnshardedCI(t testing.TB) {
+	if cibuild.On() && os.Getenv("TS_TEST_SHARD") == "" {
+		t.Skip("skipping on CI without TS_TEST_SHARD")
+	}
+}
+
 var serializeParallel = envknob.RegisterBool("TS_SERIAL_TESTS")
 
 // Parallel calls t.Parallel, unless TS_SERIAL_TESTS is set true.