Modify limits fields according to microversion

1. Some limits fields are removed from Microversion 2.35/2.38/2.56,
   so we should check limits fields according to microversion.
2. In test_max_metadata_exceed_limit, maxImageMeta is deprecated from
   Microversion 2.38, so maxServerMeta is used instead, btw, maxServerMeta
   seems to be more suitable for this testcase.
   Besides, test_max_metadata_exceed_limit is not used in interop, so we
   can safely change its name.

ref: https://developer.openstack.org/api-ref/compute/#show-rate-and-absolute-limits

Implements blueprint: clear-deprecated-api

Change-Id: I53e2ee82c9c52afb0a56526c655eb9b3b6b8f483
9 files changed