build_library: Shrink the sysext-python image by removing python tests

Do the same thing we did for GCE and Azure.

build_library/sysext_mangle_flatcar-python

@@ -7,4 +7,14 @@ pushd "${rootfs}"
 
 rm -rf ./usr/{lib/debug,share,include,lib64/pkgconfig}
 
+# Remove test stuff from python - it's quite large.
+for p in ./usr/lib/python*; do
+    if [[ ! -d ${p} ]]; then
+        continue
+    fi
+    # find directories named tests or test and remove them (-prune
+    # avoids searching below those directories)
+    find "${p}" \( -name tests -o -name test \) -type d -prune -exec rm -rf '{}' '+'
+done
+
 popd