usertools: replace string.split
usertools: replace string.split

In python3 the standard way to split strings is to use the
split() on the string object itself. The old way is broken
and would cause a traceback.

Signed-off-by: Stephen Hemminger <06fa905d7f2aaced6dc72e9511c71a2a51e8aead@networkplumber.org>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk