set memory_static_min and memory_static_max different from base memory
change hash keys to better comprehension
less verbose conversion from MB to B
change memory key to memory_target
refactor update_guest to accept cpus attributes
refact memory key on update_guest method
add support to set number of cpus without shutdown virtual machine
add support to set memory amount without shutdown virtual machine
New conditional to check memory parameter

- In case of user does not send memory has dict we are going to set it
  for him.
Change the way we get info from dict to avoid KeyError
New conditional to check cpus parameter

- In case of user does not send cpus has dict we are going to set it
  for him.
Fix error on setting VCPUs values

- It seems to be a bug on XenServer.
  (https://github.com/OpenXenManager/openxenmanager/issues/10)
  The VCPUs_max must be bigger or egual VCPUs_at_startup
Remove debugger line
The VCPUs_max must be bigger or egual VCPUs_at_startup. So, we gotta to set max first
Convert number to string

- Xen just accept string values