Update login-flow to account for development environments

[gwwar]

I was running some tests locally and noticed some failures for local runs, because we visit devdocs instead of the reader after login. I added a check there to account for the case, but let me know if there's something better to compare against.

Testing Instructions

Try to run the wp-invite-users-spec.js against a local calypso instance, and the config using "calypsoBaseURL": "http://calypso.localhost:3000",

[bsessions85]

Failed test is unrelated.

[bsessions85]

Merging so it doesn't get stale

[gwwar]

Thanks @bsessions85 !