engine: Unclear event log when failing on removing Neutron network from VM

The Timeout exception happened before the parameters of the audit log were
initialized.
Moved the initialization to the beginning of the execution
(before new 'ExternalNetworkManager(iface).deallocateIfExternal()').

Change-Id: I924ee1f749b74203e80a088d2ec5e4e888fe0221
Bug-Url: https://bugzilla.redhat.com/1102572
Signed-off-by: Alona Kaplan <alkaplan@redhat.com>