convert min_count and max_count to type int in nova v3 api

this converts min_count and max_count to type:int in nova
v3 api.
If the string type hasn't been converted, in the method
_check_num_instances_quota of nova/compute/api.py, something
like req_ram = '2'*128 will occur. That's why the issue in
bug 1254616 arise.

Change-Id: I567b249e7a30681980ed760d5d09aad4c8e603b9
Closes-bug: 1254616
Merge "convert min_count and max_count to type int in nova v3 api"