Have nicer error when config or env arent found

[viglesiasce]

Currently if the environment or config file is not found we bail out in a nasty stack trace. We should catch this and provide a useful error message:

[root@h-01 ~]# euca-deploy uninstall -e shared-setup-1.yml 
Traceback (most recent call last):
  File "/usr/bin/euca-deploy", line 5, in <module>
    pkg_resources.run_script('Euca-Deploy==0.1a', 'euca-deploy')
  File "/usr/lib/python2.6/site-packages/pkg_resources.py", line 461, in run_script
    self.require(requires)[0].run_script(script_name, ns)
  File "/usr/lib/python2.6/site-packages/pkg_resources.py", line 1194, in run_script
    execfile(script_filename, namespace, namespace)
  File "/usr/lib/python2.6/site-packages/Euca_Deploy-0.1a-py2.6.egg/EGG-INFO/scripts/euca-deploy", line 23, in <module>
    args.branch)
  File "/usr/lib/python2.6/site-packages/Euca_Deploy-0.1a-py2.6.egg/eucadeploy/componentdeployer.py", line 16, in __init__
    self.config = self.read_config()
  File "/usr/lib/python2.6/site-packages/Euca_Deploy-0.1a-py2.6.egg/eucadeploy/componentdeployer.py", line 41, in read_config
    return yaml.load(open(self.config_file).read())
IOError: [Errno 2] No such file or directory: 'etc/config.yml'