devtool: Fix build-sdk when pn doesn't match filename

If an image with the filename foo.bb could be built using the name "bar"
instead, then build-sdk would fail to create the derivative sdk.

This was because the code assumed that the file name matched the target,
which is not necessarily the case.

(From OE-Core rev: d58a326b6960be14b8a049253559aec9582b7d0d)

Signed-off-by: Randy Witt <randy.e.witt@linux.intel.com>
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/devtool

@@ -86,6 +86,11 @@ class ConfigHandler(object):
         with open(self.config_file, 'w') as f:
             self.config_obj.write(f)
 
+    def set(self, section, option, value):
+        if not self.config_obj.has_section(section):
+            self.config_obj.add_section(section)
+        self.config_obj.set(section, option, value)
+
 class Context:
     def __init__(self, **kwargs):
         self.__dict__.update(kwargs)