package_manager.py: check the result of create_index
While invoking create_index failed, there was no error output
and didn't break the build until the package installation.
...
|ERROR: run-postinsts not found in the base feeds (qemux86 i586 x86
noarch any all).
...
The reason is we used multiprocessing to execute create_index, and
did not check its invoking result.
Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
