core: OpenstackNetworkProviderProperties#equals

OpenstackNetworkProviderProperties.equals(Object) was broken in patch
Ib12a76a069d1d4b5c6cac642bfe6a3da1338a4c5 when pluginType was changed
from OpenstackNetworkPluginType which can use "!=" since it's an enum
to a String.

This patch fixes the equals(Object) method by using !equals instead of
!=.

Change-Id: Idac272b69c9460a9d56192fc9ddc1ae81de3a331
Signed-off-by: Allon Mureinik <amureini@redhat.com>