virttest.base_installer:Fix the module_list errors

As the new arch support for autotest, the style of kvm module list
has changed from "kvm kvm-intel" to ["kvm", "kvm-intel"]. See the
commit 126491bbf7cb3f1b499d4f24079c988b7c798d29 and
       6adc92e6949b960a190c59c27f5cb97e1f332605

so the module_list can't call split().

Signed-off-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>