Raising NoCredentialsException on utils#find_api_key

NoCredentialsException is a ClickException, which is handled nicely by
click, displaying the error msg and returning an exit code != 0.

shub/exceptions.py

@@ -0,0 +1,5 @@
+from click import ClickException
+
+
+class NoCredentialsException(ClickException):
+    pass

shub/utils.py

@@ -10,6 +10,7 @@
 import requests
 
 from shub.click_utils import log
+from shub.exceptions import NoCredentialsException
 
 SCRAPY_CFG_FILE = os.path.expanduser("~/.scrapy.cfg")
 OS_WIN = True if os.name == 'nt' else False
@@ -28,10 +29,20 @@ def missing_modules(*modules):
 
 
 def find_api_key():
-    """Finds and returns the Scrapy Cloud APIKEY"""
+    """Finds and returns the Scrapy Cloud APIKEY
+
+    Raises:
+        NoCredentialsException: if no API key is found
+    """
     key = os.getenv("SHUB_APIKEY")
     if not key:
         key = get_key_netrc()
+
+    if not key:
+        err = ("Your credentials haven't been defined.\n"
+               "Use 'shub login' or set the SHUB_APIKEY environment variable.")
+        raise NoCredentialsException(err)
+
     return key