Don't use bare except when importing (#667)

Using a bare except statement when importing hides other errors, which
then get lost when the next import fails.

Co-authored-by: Ed Singleton <[email protected]>

msal/mex.py

@@ -27,7 +27,7 @@
 
 try:
     from urllib.parse import urlparse
-except:
+except ImportError:
     from urlparse import urlparse
 try:
     from xml.etree import cElementTree as ET