CLEANUP: ssl/cli: use a local context for "show cafile"

CLEANUP: ssl/cli: use a local context for "show cafile"

Saying that the layout and usage of the various variables in the ssl
applet context is a mess would be an understatement. It's very hard
to know what command uses what fields, even after having moved away
from the mix of cli and ssl.

Let's extract the parts used by "show cafile" into their own structure.
Only the "show_all" field would be removed from the ssl ctx, the other
fields are still shared with other commands.