yocto-check-layer: show the distro used

It is good to know which distribution is being used, because it is not the same
whether we are using the poky or openembedded-core+bitbake repository.

The default distribution of bitbake is the nodistro while the other is poky.
The nodistro and poky produce different results when used to check the compatibility
of a layer so it is important to inform about the distro in use.

(From OE-Core rev: bcc74229e6d5a716a9f65546665a42478295dece)

Signed-off-by: Jose Quaresma <jose.quaresma@oss.qualcomm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/yocto-check-layer

@@ -35,6 +35,7 @@ logger = scriptutils.logger_create(PROGNAME, stream=sys.stdout)
 def test_layer(td, layer, test_software_layer_signatures):
     from checklayer.context import CheckLayerTestContext
     logger.info("Starting to analyze: %s" % layer['name'])
+    logger.info('Distro: %s' % td['bbvars']["DISTRO"])
     logger.info("----------------------------------------------------------------------")
 
     tc = CheckLayerTestContext(td=td, logger=logger, layer=layer, test_software_layer_signatures=test_software_layer_signatures)