Handle env variable expansion errors better in config parsing

Also, change all instances of 'environmental variables' to 'environment
variables', as that is the accepted terminology (which I didn't know up
to this point!)

Author: xanarin

scuba/config.py

@@ -268,9 +268,13 @@ def _get_volumes(data):
 def _expand_path(in_str):
     try:
         output = expand_env_vars(in_str)
-    except (KeyError, ValueError):
+    except KeyError as ke:
         # pylint: disable=raise-missing-from
-        raise ConfigError("Unset environmental variable used in '{}'".format(in_str))
+        raise ConfigError("Unset environment variable '{}' used in '{}'".format(ke.args[0], in_str))
+    except ValueError as ve:
+        raise ConfigError("Unable to expand string '{}' due to parsing "
+                "errors".format(in_str)) from ve
+
     return output
 
 class ScubaVolume:

scuba/utils.py

@@ -82,7 +82,7 @@ def writeln(f, line):
     f.write(line + '\n')
 
 def expand_env_vars(in_str):
-    """Expand environmental variables in a string
+    """Expand environment variables in a string
 
     Can raise `KeyError` if a variable is referenced but not defined, similar to
     bash's nounset (set -u) option"""

tests/test_config.py

@@ -885,7 +885,7 @@ def test_alias_volumes_set(self):
         assert v.options == ['z', 'ro']
 
     def test_volumes_with_env_vars_simple(self):
-        '''volume definitions can contain environmental variables'''
+        '''volume definitions can contain environment variables'''
         os.environ["TEST_VOL_PATH"] = "/bar/baz"
         os.environ["TEST_VOL_PATH2"] = "/moo/doo"
         with open('.scuba.yml', 'w') as f:
@@ -906,7 +906,7 @@ def test_volumes_with_env_vars_simple(self):
         assert v.options == []
 
     def test_volumes_with_env_vars_complex(self):
-        '''complex volume definitions can contain environmental variables'''
+        '''complex volume definitions can contain environment variables'''
         os.environ["TEST_HOME"] = "/home/testuser"
         os.environ["TEST_TMP"] = "/tmp"
         os.environ["TEST_MAIL"] = "/var/spool/mail/testuser"