camkes-vm: avoid exception when BAMBOO is not set

Since we are enumerating builds, it is possible that BAMBOO is not set,
leading to an exception when deleting this (unused) key. Therefore check
for presence before deleting.

Signed-off-by: Gerwin Klein <gerwin.klein@proofcraft.systems>

camkes-vm/build.py

@@ -28,7 +28,8 @@ def run_build(manifest_dir: str, build: Build):
 
     build.files = plat.image_names(build.get_mode(), "capdl-loader")
     build.settings['CAMKES_VM_APP'] = build.app or build.name
-    del build.settings['BAMBOO']    # not used in this test, avoid warning
+    if 'BAMBOO' in build.settings:
+        del build.settings['BAMBOO']    # not used in this test, avoid warning
 
     if plat.arch == 'x86':
         del build.settings['PLATFORM']  # not used for x86 in this test, avoid warning