Parameterize master.conf location.

[arensb]

I've added a parameter that allows the user to specify the location of the master.conf file using an environment variable:

arensb@4dc1304

[MarvAmBass]

Hi Andrew, thanks for you work! I really appreciate it!

Does this really work? You just moved the location into a env right? But if you supply this env from outside the container it gets overwritten with the same value as before - am I right?
Isn't there a check needed to only set this variable if it's not already set?

Thanks!