distro_identifier: replace slash with hyphen

Use "-" instead of "/" in "n/a" strings ("Distributor ID" and/or
"Release"), provided by `lsb_release`.
This leads to directories and subdirectories created in ./sstate-cache/
e.g. Distro-n/a/ where "Distro-n" is dir and "a" is subdir.

(From OE-Core rev: c2a9f0c330f0da82792f87e3860b06c25b986983)

Signed-off-by: Mihai Lindner <mihaix.lindner@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oe/lsb.py

@@ -31,4 +31,4 @@ def distro_identifier(adjust_hook=None):
         distro_id, release = adjust_hook(distro_id, release)
     if not distro_id:
         return "Unknown"
-    return '{0}-{1}'.format(distro_id, release).replace(' ','-')
+    return '{0}-{1}'.format(distro_id, release).replace(' ','-').replace('/','-')