log: process.py: fix weird space in stdout/stderr log output

Log output before:

  stdout:
   | line1
  | line2
  | line3

After:

  stdout:
  | line1
  | line2
  | line3

Change-Id: I4202e7dfbb550acaf55a6c6487fc07819ab18b94
diff --git a/src/osmo_gsm_tester/core/process.py b/src/osmo_gsm_tester/core/process.py
index bff8dba..9cde7de 100644
--- a/src/osmo_gsm_tester/core/process.py
+++ b/src/osmo_gsm_tester/core/process.py
@@ -291,13 +291,13 @@
         m = self.get_stdout_tail(prefix='| ')
         if not m:
             return
-        self.log('stdout:\n', m, '\n')
+        self.log('stdout:', '\n' + m, '\n')
 
     def log_stderr_tail(self):
         m = self.get_stderr_tail(prefix='| ')
         if not m:
             return
-        self.log('stderr:\n', m, '\n')
+        self.log('stderr:', '\n' + m, '\n')
 
     def close_output_logs(self):
         for k, v in self.outputs.items():