lib/oe/path: Add canonicalize()

oe.path.canonicalize() is used to canonicalize paths (i.e., remove
symbolic links and "..", and make them absolute). It takes a string
with paths separated by commas, and returns the canonicalized path in
the same format.

Signed-off-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 282b19c0)
Signed-off-by: Steve Sakoman <steve@sakoman.com>