Re-prioritize how access_token() finds the token to use
Re-prioritize how access_token() finds the token to use

This makes access_token() use the passed params first, before looking
in environment variables and files.

Making this change to handle the case when you usually are happy with
your env vars or file, but want to use a different token as a one-off
when testing.

mgoffin/ThreatExchange,wxsBSD/ThreatExchange,theCatWisel/ThreatExchange,tiegz/ThreatExchange,mgoffin/ThreatExchange,RyPeck/ThreatExchange,tiegz/ThreatExchange,tiegz/ThreatExchange,tiegz/ThreatExchange,RyPeck/ThreatExchange,RyPeck/ThreatExchange,wxsBSD/ThreatExchange,RyPeck/ThreatExchange,wxsBSD/ThreatExchange,mgoffin/ThreatExchange,RyPeck/ThreatExchange,tiegz/ThreatExchange,mgoffin/ThreatExchange,wxsBSD/ThreatExchange,theCatWisel/ThreatExchange,theCatWisel/ThreatExchange,mgoffin/ThreatExchange,wxsBSD/ThreatExchange,theCatWisel/ThreatExchange,wxsBSD/ThreatExchange,theCatWisel/ThreatExchange,RyPeck/ThreatExchange,theCatWisel/ThreatExchange,mgoffin/ThreatExchange,tiegz/ThreatExchange