binman: Fix unique names having '/.' for images read from files

binman: Fix unique names having '/.' for images read from files

Binman can embed a copy of the image description into the images it
builds as a fdtmap entry, but it omits the /binman/<image-name> prefix
from the node paths while doing so. When reading an already-built image
file, entries are reconstructed using this fdtmap and their associated
nodes still lack that prefix.

Some entries like fit and vblock create intermediate files whose names
are based on an entry unique name. This name is constructed from their
node's path by concatenating the parents with dots up to the binman
node, e.g. /binman/image/foo/bar becomes 'image.foo.bar'.

However, we don't have this /binman/image prefix when replacing entries
in such an image. The /foo/bar entry we read when doing so erroneously
has the unique name of '/.foo.bar', causing permission errors when the
entry attempts to create files based on that.

Fix the unique-name generation by stopping at the '/' node like how it
stops at the binman node. As the unique names are used as filenames, add
tests that check if they're safe to use as filenames.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>