virttest.virsh: Add emulatorpin command wrapper function

Signed-off-by: Alex Jia <ajia@redhat.com>
virttest.libvirt_xml.vm_xml: Add XML manipulation method for emulatorpin and placement of the vcpu

Signed-off-by: Alex Jia <ajia@redhat.com>
virttest.utils_test: Add common CPUs parser function

Signed-off-by: Alex Jia <ajia@redhat.com>
libvirt.tests: Sync new common CPUs parser function

Signed-off-by: Alex Jia <ajia@redhat.com>
libvirt.tests: Add test cases for virsh emulatorpin

Signed-off-by: Alex Jia <ajia@redhat.com>