Use "commit" for rollbacks instead of "execute".

Fix a couple lingering references to "executing" rollbacks. We've long
since switched to the terminology "commit", to highlight that a staged
rollback that has been committed will not take effect until the device
reboots.

Fixes: 136044234
Test: atest RollbackTest
Change-Id: Ic364778c253ff59af8206824a66df72569ab1307