timer_management: Re-write test and add more cases

1. No need test all VMs on the host, run cases against one VM is enough.
2. Merge functions which has similar structures and steps.
3. Add more cases to cover specific timer name and 'present' value.

Signed-off-by: Yanbing Du <ydu@redhat.com>
Merge pull request #323 from will-Do/timer

timer_management: Re-write test and add more cases