cassini-ci: Upload ptest-runner logs to JFrog

Current LAVA test framework (inline test action) needs to run
`transfer_overlay` action if there are any shell commands in the
inline test action. In order for `transfer_overlay` to work `root`
account is required because, overlay is done at `/`. Therefore,
issue `sudo su -` after log in as `cassini` user.

Signed-off-by: Devaraj Ranganna <devaraj.ranganna@arm.com>