tst_test.sh: TCONF on basename error when setting TST_ID

'basename $0' fails when loaded in command line with bash (at least)
as $0 is invalid ('-bash'):

    $ unset TST_ID; export TST_NO_DEFAULT_RUN=1; . tst_test.sh
    -bash: tst_ansi_color.sh: No such file or directory
    basename: invalid option -- 'b'
    Try 'basename --help' for more information.

It's better to TCONF than be without TST_ID.

NOTE: Sourcing tst_test.sh can be needed for network scripts: users
might want to set network variables with tst_net.sh, which itself
sources tst_test.sh.

Reviewed-by: Li Wang <liwang@redhat.com>
Signed-off-by: Petr Vorel <pvorel@suse.cz>

testcases/lib/tst_test.sh

@@ -377,7 +377,8 @@ tst_run()
 }
 
 if [ -z "$TST_ID" ]; then
-	filename=$(basename $0)
+	filename=$(basename $0) || \
+		tst_brk TCONF "Failed to set TST_ID from \$0 ('$0'), fix it with setting TST_ID before sourcing tst_test.sh"
 	TST_ID=${filename%%.*}
 fi
 export TST_ID="$TST_ID"