lib/configfragments: when disabling fragments, treat fragment names as prefixes if...

lib/configfragments: when disabling fragments, treat fragment names as prefixes if they end with /

This allows disabling classes of fragments without knowing their full names, e.g.
instead of

$ bitbake-config-build disable-fragment machine/qemuarm

one can issue

$ bitbake-config-build disable-fragment machine/

to match and disable everything that starts with 'machine/'.

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>