bugfix: spack config get <section> in environments

`spack config get <section>` was erroneously returning just the `spack.yaml`
for the environment.

It should return the combined configuration for that section (including
anything from `spack.yaml`), even in an environment.

- [x] reorder conditions in `cmd/config.py` to fix

lib/spack/spack/cmd/config.py

@@ -143,7 +143,10 @@ def config_get(args):
     """
     scope, section = _get_scope_and_section(args)
 
-    if scope and scope.startswith('env:'):
+    if section is not None:
+        spack.config.config.print_section(section)
+
+    elif scope and scope.startswith('env:'):
         config_file = spack.config.config.get_config_filename(scope, section)
         if os.path.exists(config_file):
             with open(config_file) as f:
@@ -151,9 +154,6 @@ def config_get(args):
         else:
             tty.die('environment has no %s file' % ev.manifest_name)
 
-    elif section is not None:
-        spack.config.config.print_section(section)
-
     else:
         tty.die('`spack config get` requires a section argument '
                 'or an active environment.')