Patching virttest to facilitate the test of hugepage feature

Aim to make the guest using hugepages, adding memoryBacking tag in libvirt_xml/vm_xml.
Further, adding functions used to get/set the parameter of hugepage in virttest.staging.utils_memory .
These two functions looks the similar. And for huge page there is more options that we may want to get from procfs. So should we update the exist function read_from_meminfo() in the same file and just call it in these two functions?