agent: Remove the main() method from LibvirtComputingResource

Seems like very ancient code which is not needed.
agent: Do not define domains persistent in libvirt

We used to define domains persistent in libvirt, which caused XML definitions
to stay there after a reboot of the hypervisor.

We however don't do anything with those already defined domains, actually, we wipe
all defined domains when starting the agent.

Some users however reported that libvirt started these domains after a reboot
before the CloudStack agent was started.

By starting domains from the XML description and not defining them we prevent
them from ever being stored in libvirt.
agent: Rename startDomain to startVM

The other methods are called stopVM and rebootVM, so it makes
sence to use startVM.
Summary: Remove superfluous chroot and change to use standard jre

Detail: Since the script executes inside the running vm, the chroot is not necessary. Also the standard jre is used instead of sun jre.

BUG-ID: CLOUDSTACK-1066
Signed-off-by: Chiradeep Vittal <chiradeep@apache.org> 1360277071 -0800