Fix inconsistent type of default value
Fix inconsistent type of default value

The provider_net_base_segmentation_id parameter is StrOpt, thus expects
a string value. This change fixes the incorrect type(integer) of
its default value to get rid of the following warning message.

/usr/lib/python3.6/site-packages/oslo_config/types.py:59: UserWarning:
 converting '3000' to a string
  warnings.warn('converting \'%s\' to a string' % str_val)

Closes-Bug: #1959859
Change-Id: I92aeb04f6c5aefd26e83b83c17d80341418aa233

openstack/tempest,openstack/tempest