micro version not able to handle V3.1

[Sheel Rana]

Seems some issue in cinder/api/openstack/api_version_request.py

If we pass ("3.1", None), some sample debug prints:

ver_major= 1
ver_minor= 0
ver_major= 2
ver_minor= 0
ver_major= 3
ver_minor= 0

Request parameters:
GET /v3/fake/volumes HTTP/1.0
Openstack-Volume-Microversion: 3.1

versionString=3.1
major_Version extracted=3
minor_Version extracted=1
API Version Request Major: 3, Minor: 1

How to reproduce:

Step 1: update Max_Version field in "cinder/api/openstack/api_version_request.py"

_MIN_API_VERSION = "3.0"
_MAX_API_VERSION = "3.1"

Step 2: Run below test case to check latest version:

class V3TestCase(test.TestCase):

    def setUp(self):
        super(self.__class__, self).setUp()
        self.controller = volumes.VolumeController('VolumeActions')

    @mock.patch.object(vol, 'check_volume_filters_strict')
    def test_check_volume_filters_strict(self, filter_volume):
        print("Test Start")
        volume_api = cinder.volume.api.API()
        req = fakes.HTTPRequest.blank('/fake/volumes', base_url='http://localhost/v3')
        req.method = 'GET'
        req.content_type = 'application/json'
        req.headers = {version_header_name: 3.1}
        response = self.controller.index(req)
        self.assertTrue(filter_volume.called)

tox -epy27 -- --no-discover cinder.tests.unit.test_volume.V3TestCase.test_check_volume_filters_strict