shifts code order on 'build dependencies'

It's a minor issue but shouldn't virtualenv and requirements.txt installation come before running "bin/mkt whoami [your github user name]"? 
Reason: error for not having "netifaces" installed from "requirements.txt" yet if you don't already have it installed globally

```
$ bin/mkt whoami marcoagner
Traceback (most recent call last):
  File "bin/mkt", line 3, in <module>
    import cmds
  File "/Users/marcoagner/Projects/marketplace-env/mkt/cmds.py", line 13, in <module>
    import netifaces
ImportError: No module named netifaces
```