[devices] Add time for powercycle

PDU reboots take longer than I expected; we'll need to spam the
serial line for longer.

Change-Id: I88a1a9cecb9ec786e9a0ecb9c8d3c4432cfa0d5b
diff --git a/devices/power.go b/devices/power.go
index f2f1461..d25c11e 100644
--- a/devices/power.go
+++ b/devices/power.go
@@ -137,7 +137,7 @@
 
 	// Spam the serial line to get into fastboot mode.
 	// We spam the line so much because it gives us the greatest chance of entering fastboot.
-	for i := 1; i < 5000; i++ {
+	for i := 1; i < 15000; i++ {
 		if _, err := io.WriteString(serial, "\nf\n"); err != nil {
 			return err
 		}