Hard-coded key value causing issue with browserstack-local.js

[mccataldo]

In scripts/browserstack.js:10 the value for password is
process.env.BROWSERSTACK_ACCESS_KEY || config.bs_key
but in scripts/browserstack-local.js:14 the value for key is
process.env.BROWSERSTACK_ACCESS_KEY
which results in hard-coded values in testem.json only pass into the first file and not the second.
Furthermore, this isn't apparent in the stack trace when testem fails but only when running browserstack-local.js directly (invoked by testem).