Use 'tempest run --slowest' in integrated-compute (again)

Change I53b0fa6dcf077191565e2aaf3f08a24b3238a34b added the --slowest
option to the tempest run command for scenario and serial tests but
missed adding it when running api tests.

The --slowest option will show a list of the slowest tests after the
tests finish running.

Change-Id: Ia5a995121748a2c244f060e6ce4b395213bb196e
1 file changed