Converted VM_CPUS and VM_MEMORY to int

Converted VM_CPUS and VM_MEMORY to int

When VM_CPUS and VM_MEMORY are taken from configuration file they have
to be converted to int to avoid this traceback:

Traceback (most recent call last):
  File "/var/lib/jenkins/jobs/image-creator/workspace/jenkins-scripts/job_imager.py", line 142, in <module>
    sys.exit(main())
  File "/var/lib/jenkins/jobs/image-creator/workspace/jenkins-scripts/job_imager.py", line 94, in main
    os.getenv("VM_CPUS", 8), basedir)
  File "/var/lib/jenkins/jobs/image-creator/workspace/jenkins-scripts/job_imager.py", line 33, in run_inside_vm
    (vm_memory, vm_cpus, vm_image, basedir)
TypeError: %d format: a number is required, not str

Change-Id: Ib18cbd320f013e8b3d9075dadf22840131e07bc1
Signed-off-by: Ed Bartosh <eduard.bartosh@intel.com>