refstack: add manually method to let user can set its tempest.conf and defcore.txt

refstack: add manually method to let user can set its tempest.conf and defcore.txt

JIRA: DOVETAIL-394

for refstack, userguide is listed in https://gerrit.opnfv.org/gerrit/#/c/33049/
in CI, use the automate way to generate tempest.conf to let refstack run against SUT, i.e., defcore.tc001.yml
will provide a way to let user can let refstack run against SUT manually, i.e. defcore.tc002.yml
since the tempest.conf autometely generated may not satisfied with SUT, users can adjust its tempest.conf to let the defcore testcases pass.

Change-Id: I5ed212c9c6d864d352d1c497ea039cc553461158
Signed-off-by: MatthewLi <matthew.lijun@huawei.com>