Update SystemdService.exists to find all unit files

Author: CarstenGrohmann

testinfra/modules/service.py

@@ -169,15 +169,21 @@ class SystemdService(SysvService):
 
     def _has_systemd_suffix(self):
         """
-        Check if service name has a known systemd unit suffix
+        Check if the service name has a known systemd unit suffix
         """
         unit_suffix = self.name.split(".")[-1]
         return unit_suffix in self.suffix_list
 
     @property
     def exists(self):
-        cmd = self.run_test('systemctl list-unit-files | grep -q "^%s"', self.name)
-        return cmd.rc == 0
+        # systemctl return codes:
+        #   0: unit is active
+        #   1: unit not failed (used by is-failed)
+        #   2: unused
+        #   3: unit is not active
+        #   4: no such unit
+        cmd = self.run_expect([0, 1, 3, 4], "systemctl status %s", self.name)
+        return cmd.rc < 4
 
     @property
     def is_running(self):