snapcraft close should complain early with one argument

[Adam Collard]

I find myself accidentally omitting the snap name quite often with snapcraft and didn't notice my mistake when attempting to close a branch using:

⟫ snapcraft close edge/bump-20
Your account lacks permission to close channels for this snap. Make sure the logged in account has upload permissions on 'edge/bump-20' in series '16'.

snapcraft knows that 'close' needs at least two arguments and additionally it should know that '/' is not a valid character for a snap name. By applying this knowledge, snapcraft could help me realise my typo.

Bonus points if it inspects the current directory for a snapcraft.yaml and suggests the right command to me.

[Daniel Manrique (roadmr)]

This has happened to users in the wild:

https://forum.snapcraft.io/t/unable-to-close-channel-in-a-track/7063/4

https://forum.snapcraft.io/t/firefox-please-create-the-track-esr/5006/22

Other than Adam's suggestion, perhaps the error message template can be changed to clearly indicate it's talking about the *snap* name, not the channel.

diff --git a/snapcraft/storeapi/errors.py b/snapcraft/storeapi/errors.py
index 709b204a..25ef0b9f 100644
--- a/snapcraft/storeapi/errors.py
+++ b/snapcraft/storeapi/errors.py
@@ -598,8 +598,8 @@ class StoreChannelClosingPermissionError(StoreError):

     fmt = (
         'Your account lacks permission to close channels for this snap. Make '
- 'sure the logged in account has upload permissions on {snap_name!r} '
- 'in series {snap_series!r}.'
+ 'sure the logged in account has upload permissions on the '
+ '{snap_name!r} snap in series {snap_series!r}.'
     )

     def __init__(self, snap_name, snap_series):