MINOR: ssl/cli: display more filenames in 'show ssl cert'

MINOR: ssl/cli: display more filenames in 'show ssl cert'

"show ssl cert <file>" only displays a unique filename, which is the
key used in the ckch_store tree. This patch extends it by displaying
every filenames from the ckch_conf that can be configured with the
crt-store.

In order to be more consistant, some changes are needed in the future:
- we need to store the complete path in the ckch_conf (meaning with
  crt-path or key-path)
- we need to fill a ckch_conf in cases the files are autodiscovered