[SmokeTest] Add request mode choice

[SmokeTest] Add request mode choice

Smoke tests can be run with normal or global user.
Normal user is created in environment SetUp() and
is deleted in TearDown() method. Normal user name
is "smokeuser".

You can run tests by normal user with flags:
-u or --request_mode=user
You can run tests by global user with flags:
-g or --request_mode=global

Without above flags tests are run with global user
by default

Change-Id: Ibf6e195dd21c78f1c7d19c45c4fa0753ec1baf7f