[ssl_mgmt] Use nobody to test email

nobody should be present on most (all?) unix system and is thus better
for test. However it's still not ideal as it might be connected to an
account that is not the one running the testsuite and the mail might
surprise that user.

ssl_mgmt/tests/ssl_mgmt.conf

@@ -21,4 +21,4 @@ rootCAPwdPath=./root_ca
 
 managedCerts=./managed_certs
 
-notifiedUsers=robotux
+notifiedUsers=nobody