Update oslo-incubator processutils module

Changes -
 * Fix exception message in openstack.common.processutils.execute
 * Remove `processutils` dependency on `log`
 * Fix broken formatting of processutils.execute log statement
 * Move nova.utils.cpu_count() to processutils module

Change-Id: Ic4b65ffc35ecea3580c984e5417e1ecdcf9c95ca
Merge "Update oslo-incubator processutils module"