fix violation of import rule in TestAPI

fix violation of import rule in TestAPI

TestAPI violate import rule of OpenStack Style a lot, like
Do not import objects, only modules
Do not import more than one module per line
Alphabetically order your imports by the full module path
This patch is mean to fix them.

Change-Id: Ia05b944a74b3f443c9101a9840f613f9a6f5ae49
Signed-off-by: SerenaFeng <feng.xiaowei@zte.com.cn>