[Test] Fix build_bin_path for case sensitive FS

Match xenia-build and premake configuration and platform capitalization with
only first letter capitalized in filesystem (Debug, Checked, Released, Linux,
Windows, etc).
Fix xenia-build test command on linux systems.

xenia-build

@@ -389,7 +389,7 @@ def get_build_bin_path(args):
         platform = 'windows'
     else:
         platform = 'linux'
-    return os.path.join(self_path, 'build', 'bin', platform, args['config'])
+    return os.path.join(self_path, 'build', 'bin', platform.capitalize(), args['config'].capitalize())
 
 
 def discover_commands(subparsers):