Remove utils.reset_is_neutron() to avoid races

If a unit test does not call utils.reset_is_neutron() when
it is complete, it may introduce a race condition because
the utils.is_neutron() value is cached to the old result.

This patch removes the utils.reset_is_neutron() and instead
makes sure that we never have a cached value for it.  It
also refactors _is_neutron out of vmwareapi.VMOps because
it cache the result unnecessarily.

Change-Id: I2440e308b00979b31c750513d14608808a295c33
Closes-Bug: #1309043
Merge "Remove utils.reset_is_neutron() to avoid races"