pytest: Stabilize test_autocleaninvoice

The RPC calls aren't really free, so let's wait for absolute times, computed
from the `start_time` instead.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

tests/test_lightningd.py

@@ -425,6 +425,7 @@ class LightningDTests(BaseLightningDTests):
     def test_autocleaninvoice(self):
         l1 = self.node_factory.get_node()
 
+        start_time = time.time()
         l1.rpc.autocleaninvoice(cycle_seconds=8, expired_by=2)
 
         l1.rpc.invoice(msatoshi=12300, label='inv1', description='1', expiry=4)
@@ -435,7 +436,7 @@ class LightningDTests(BaseLightningDTests):
         assert len(l1.rpc.listinvoices('inv1')['invoices']) == 1
         assert len(l1.rpc.listinvoices('inv2')['invoices']) == 1
 
-        time.sleep(6)   # total 6
+        time.sleep(start_time - time.time() + 6)   # total 6
         # Both should still be there - auto clean cycle not started.
         # inv1 should be expired
         assert len(l1.rpc.listinvoices('inv1')['invoices']) == 1
@@ -443,19 +444,19 @@ class LightningDTests(BaseLightningDTests):
         assert len(l1.rpc.listinvoices('inv2')['invoices']) == 1
         assert l1.rpc.listinvoices('inv2')['invoices'][0]['status'] != 'expired'
 
-        time.sleep(4)   # total 10
+        time.sleep(start_time - time.time() + 10)   # total 10
         # inv1 should have deleted, inv2 still there and unexpired.
         assert len(l1.rpc.listinvoices('inv1')['invoices']) == 0
         assert len(l1.rpc.listinvoices('inv2')['invoices']) == 1
         assert l1.rpc.listinvoices('inv2')['invoices'][0]['status'] != 'expired'
 
-        time.sleep(4)   # total 14
+        time.sleep(start_time - time.time() + 14)   # total 14
         # inv2 should still be there, but expired
         assert len(l1.rpc.listinvoices('inv1')['invoices']) == 0
         assert len(l1.rpc.listinvoices('inv2')['invoices']) == 1
         assert l1.rpc.listinvoices('inv2')['invoices'][0]['status'] == 'expired'
 
-        time.sleep(4)   # total 18
+        time.sleep(start_time - time.time() + 18)   # total 18
         # Everything deleted
         assert len(l1.rpc.listinvoices('inv1')['invoices']) == 0
         assert len(l1.rpc.listinvoices('inv2')['invoices']) == 0