cassini-[ci,test]: Fix user access issue for tests

Run the ptest-runner as a `test` user rather than root, this fixes the
issue with the user access where `bats` is being invoked as a `test`
user by ptest framework running as `root`

All ptest-runner suites should be invoked as `test` user

The `test` user should be able to access necessary drivers and not
require `root` access

Signed-off-by: Vikas Katariya <vikas.katariya@arm.com>