testimage/testsdk/selftest: Avoid platform.distro_identifier deprecation warnings

Use our own lsb function instead as used elsewhere by the codebase.

(From OE-Core rev: acac45a6fd604d28ef7c23d67482af3d7e8bcfe3)

(From OE-Core rev: 570256a64af5a3fa994a20a5cc4c74d59ffc361f)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/testsdk.bbclass

@@ -23,7 +23,7 @@ def get_sdk_configuration(d, test_type):
                     'IMAGE_BASENAME': d.getVar("IMAGE_BASENAME"),
                     'IMAGE_PKGTYPE': d.getVar("IMAGE_PKGTYPE"),
                     'STARTTIME': d.getVar("DATETIME"),
-                    'HOST_DISTRO': ('-'.join(platform.linux_distribution())).replace(' ', '-'),
+                    'HOST_DISTRO': oe.lsb.distro_identifier().replace(' ', '-'),
                     'LAYERS': get_layers(d.getVar("BBLAYERS"))}
     return configuration
 get_sdk_configuration[vardepsexclude] = "DATETIME"