automated: sh-test-lib: add support for /etc/os-release file

/etc/os-release is a standard file in most distro now, [1] and [2].

Let's use it as the default mechanism to detect the distro at run time, and keep
the old mechanisms as fallback.

Also
* defines 'oe-based' name for any known OE based releases, so that we can
adapt test cases accordingly.
* convert the ID name found in /etc/os-release into the one we used to have in
lsb_release (e.g. Ubuntu vs ubuntu, ... ).

[1] https://www.freedesktop.org/software/systemd/man/os-release.html
[2] http://0pointer.de/blog/projects/os-release.html

Change-Id: I1c9e11b449f8532450c8343bc29eb0aeec58c229
Signed-off-by: Nicolas Dechesne <nicolas.dechesne@linaro.org>
1 file changed