don't hide relevant import errors (#635)

* don't hide relevant import errors

* original name

* py2 compliance

* now back to py3 compatibility....

napalm/base/__init__.py

@@ -35,7 +35,7 @@
 ]
 
 
-def get_network_driver(module_name, prepend=True):
+def get_network_driver(name, prepend=True):
     """
     Searches for a class derived form the base NAPALM class NetworkDriver in a specific library.
     The library name must repect the following pattern: napalm_[DEVICE_OS].
@@ -48,7 +48,7 @@ def get_network_driver(module_name, prepend=True):
     .. _`Read the Docs`: \
     http://napalm.readthedocs.io/
 
-    :param module_name:         the name of the device operating system or the name of the library.
+    :param name:         the name of the device operating system or the name of the library.
     :return:                    the first class derived from NetworkDriver, found in the library.
     :raise ModuleImportError:   when the library is not installed or a derived class from \
     NetworkDriver was not found.
@@ -67,16 +67,16 @@ def get_network_driver(module_name, prepend=True):
         napalm.base.exceptions.ModuleImportError: Cannot import "napalm_wrong". Is the library \
         installed?
     """
-    if module_name == "mock":
+    if name == "mock":
         return MockDriver
 
-    if not (isinstance(module_name, py23_compat.string_types) and len(module_name) > 0):
+    if not (isinstance(name, py23_compat.string_types) and len(name) > 0):
         raise ModuleImportError('Please provide a valid driver name.')
 
     # Only lowercase allowed
-    module_name = module_name.lower()
+    name = name.lower()
     # Try to not raise error when users requests IOS-XR for e.g.
-    module_install_name = module_name.replace('-', '')
+    module_install_name = name.replace('-', '')
     community_install_name = "napalm_{name}".format(name=module_install_name)
     custom_install_name = "custom_napalm.{name}".format(name=module_install_name)
     # Can also request using napalm_[SOMETHING]
@@ -87,12 +87,22 @@ def get_network_driver(module_name, prepend=True):
         try:
             module = importlib.import_module(module_name)
             break
-        except ImportError:
-            pass
+        except ImportError as e:
+            try:
+                # gotta love py23 differences
+                message = e.message
+            except AttributeError:
+                message = e.msg
+            if "No module named" in message:
+                # py2 doesn't have ModuleNotFoundError exception
+                failed_module = message.split()[-1]
+                if failed_module.replace("'", "") in module_name:
+                    continue
+            raise e
     else:
         raise ModuleImportError(
             'Cannot import "{install_name}". Is the library installed?'.format(
-                install_name=module_install_name
+                install_name=name
             )
         )