Fix unit tests using modules systems

Plus some minor fine tuning of code style.

Author: Vasileios Karakasis

reframe/core/schedulers/slurm.py

@@ -103,8 +103,7 @@ def completion_time(self, job):
             not slurm_state_completed(job.state)):
             return self._completion_time
 
-        with env.temp_environment(
-                variables=[('SLURM_TIME_FORMAT', 'standard')]):
+        with env.temp_environment(variables={'SLURM_TIME_FORMAT': 'standard'}):
             completed = os_ext.run_command(
                 'sacct -S %s -P -j %s -o jobid,end' %
                 (datetime.now().strftime('%F'), job.jobid),

unittests/test_environments.py

@@ -89,10 +89,11 @@ def test_load_restore(self):
         assert not self.environ.is_loaded
 
     @fixtures.switch_to_user_runtime
-    def test_temp_environment_context_manager(self):
-        with env.temp_environment(['testmod_foo'],
-                                  [('_var0', 'val2'),
-                                   ('_var3', 'val3')]) as environ:
+    def test_temp_environment(self):
+        self.setup_modules_system()
+        with env.temp_environment(
+                ['testmod_foo'], {'_var0': 'val2', '_var3': 'val3'}
+        ) as environ:
             assert environ.is_loaded
 
         assert not environ.is_loaded