Reduce runs in the dumpling-emperor upgrade suite.

Add + to 2-workload, 4-workload and 6-final-workload
suites.  Reduce 5-upgrade-sequence to only run two
tests and make sure upgrades to emperor occur in each
sequence.  Fix swift.yaml to not include rgw: clause
(this is already done by s3tests.yaml).

Fixes: #8051
Signed-off-by: Warren Usui <warren.usui@inktank.com>