Fix env file parsing related to quotes (#230)

This should support these cases more correctly:

```
KEY="'val'" -> {"KEY": "'val'"}
KEY="'val' something else" -> {"KEY": "'val' something else"}
```

src/everett/manager.py

@@ -295,7 +295,16 @@ def parse_env_file(envfile: Iterable[str]) -> Dict:
             raise ConfigurationError(
                 f"Invalid variable name {k!r} in env file (line {line_no + 1})"
             )
-        v = v.strip().strip("'\"")
+
+        v = v.strip()
+
+        # Need to strip matching ' and " from beginning and end--but only one
+        # round
+        for quote in "'\"":
+            if v.startswith(quote) and v.endswith(quote):
+                v = v[1:-1]
+                break
+
         data[k] = v
 
     return data
@@ -775,6 +784,9 @@ class ConfigEnvFileEnv:
         DB_HOST=localhost
         DB_PORT=5432
 
+        # CSP reporting
+        CSP_SCRIPT_SRC="'self' www.googletagmanager.com"
+
     """
 
     def __init__(self, possible_paths: Union[str, List[str]]):

tests/test_manager.py

@@ -386,16 +386,40 @@ def test_ConfigEnvFileEnv(datadir):
     assert cefe.get("loglevel") is NO_VALUE
 
 
-def test_parse_env_file():
-    assert parse_env_file(["PLAN9=outerspace"]) == {"PLAN9": "outerspace"}
+@pytest.mark.parametrize(
+    "line, expected",
+    [
+        ("PLAN9=outerspace", {"PLAN9": "outerspace"}),
+        ('KEY="val"', {"KEY": "val"}),
+        ("KEY='val'", {"KEY": "val"}),
+        # Only strips outer-most quote
+        ("KEY=\"'val'\"", {"KEY": "'val'"}),
+        ("KEY='\"val\"'", {"KEY": '"val"'}),
+        (
+            "CSP_SCRIPT_SRC='self' www.googletagmanager.com",
+            {"CSP_SCRIPT_SRC": "'self' www.googletagmanager.com"},
+        ),
+        (
+            "CSP_SCRIPT_SRC=\"'self' www.googletagmanager.com\"",
+            {"CSP_SCRIPT_SRC": "'self' www.googletagmanager.com"},
+        ),
+    ],
+)
+def test_parse_env_file_line(line, expected):
+    assert parse_env_file([line]) == expected
+
+
+def test_parse_env_file_errors():
     with pytest.raises(ConfigurationError) as exc_info:
         parse_env_file(["3AMIGOS=infamous"])
     assert str(exc_info.value) == "Invalid variable name '3AMIGOS' in env file (line 1)"
+
     with pytest.raises(ConfigurationError) as exc_info:
         parse_env_file(["INVALID-CHAR=value"])
     assert str(exc_info.value) == (
         "Invalid variable name 'INVALID-CHAR' in env file (line 1)"
     )
+
     with pytest.raises(ConfigurationError) as exc_info:
         parse_env_file(["", "MISSING-equals"])
     assert str(exc_info.value) == "Env file line missing = operator (line 2)"