When the config file isn't readable or doesn't exist, maxscale silently ends

When starting MaxScale with no commandline arguments at all and the configuration file isn't in it's default localtion or cannot be read, maxscale still silently ends. I don't know why the fix for MXS-621 didn't fix this or why the test for that didn't catch this. If the default config file is specified, maxscale does show an error as appropriate:

$ sudo chmod 600 /etc/maxscale.cnf

$ maxscale

$ maxscale -f /etc/maxscale.cnf

*

* Error : Failed to open read access to config file.

*

Note that putting the message for this in the log file is rather meaningless as we don't know what the name of that should be unless we can open the config file. I think it is best to show this message to stderr, like in the above case when the filename is specified in the -f option.