Fix filter_properties of unshelve API

When unshelving a shelved server, nova-scheduler fails because nova-conductor
of current unshelve feature passes an empty list as filter_properties, and
nova-scheduler handles it as a dict.

To fix the problem, this patch changes the filter_properties to an empty dict.

Closes-Bug: #1233563

Change-Id: I2c7a2a743a8142af0be0a182067f3295980aa997
(cherry picked from commit ef3fbe99af498a40555b44f9ef0fcf6b88eb5d30)
Merge "Fix filter_properties of unshelve API" into milestone-proposed