Revert "Add scenario 'test_preserve_preexisting_port'"

This reverts commit bedd9652206f0a33cd53a3ad51a14a22467b6604.

The newly added test is causing failures against icehouse,
reverting it for now until it's fixed.

e-r query: https://review.openstack.org/#/c/164120/

Closes-bug: #1431724
Change-Id: I224b32df50e13f0f2902f3e3921180e72681ac54
1 file changed