refstack: bugfix of testcase failure

refstack: bugfix of testcase failure

JIRA: DOVETAIL-366
JIRA: DOVETAIL-758

1)for compass, joid, failure log
  https://build.opnfv.org/ci/view/functest/job/functest-joid-baremetal-daily-master/1062/consoleFull
  https://build.opnfv.org/ci/view/functest/job/functest-compass-baremetal-daily-master/936/consoleFull
  volume_device_name should be set vdb.
  for fuel, "vdb" is used for config, drive when force_config_drive=True is in action, so set to vdc
  testcase test_attach_detach_volume is not dynamic enough, to skip temporarily.
2)rename defcore_201608.txt to defcore.txt
  since this file is the default running file, can be changed as version changes.
  and will be easy for dovetail to consume with a general name rather than a special name.
  then dovetail can define the testcases to replace this file when running.

Change-Id: I58f89095721a7bdb15230b9af2b96234c3c7dcb9
Signed-off-by: MatthewLi <matthew.lijun@huawei.com>