force full path for sendmail

tester.py

@@ -394,7 +394,7 @@ Content-transfer-encoding: utf-8
                 system_domain=system_domain,
                 system_type=system_type,
             )
-            p = subprocess.Popen(['sendmail', '-t'], stdin=subprocess.PIPE, stdout=sys.stdout.stream, stderr=sys.stderr.stream)
+            p = subprocess.Popen(['/usr/sbin/sendmail', '-t'], stdin=subprocess.PIPE, stdout=sys.stdout.stream, stderr=sys.stderr.stream)
             p.communicate(input=mail.encode('utf-8'))
             if p.returncode != 0:
                 log('Failed to send email.')