Use path fragment ~constants instead of naming every sigle path component
Use path fragment ~constants instead of naming every sigle path component

Defining named constants for every individual path component got the
strings out of the code, but actually hard-coded new assumptions
that the various locations share the same names ("containers",
"auth.json") when they may well evolve independently; and the result
was more names and more words, not more readable overall.

Instead, name the entire path fragments (path within a home directory,
within $XDG_RUNTIME_DIR), or in the case of /run/containers, the format
string.

To pay formal respect to path separators, use filepath.FromSlash.
(In practice, full Windows support would probably require at least
rethinking the assumption that at least one of $XDG_RUNTIME_DIR and
/run exists, and probably more work to conform to Windows directory
layout expectations like AppData.)

This does not change behavior.

Signed-off-by: Miloslav Trmač <9c008e38982a5397deb855345fb164f0558459ae@redhat.com>

containers/image,containers/image