util: split the virNumaGetHugePageInfoPath into separate function

util: split the virNumaGetHugePageInfoPath into separate function

https://bugzilla.redhat.com/show_bug.cgi?id=1265114

Refactor helper virNumaGetHugePageInfoPath to handle returning a directory
path when passed a page_size of 0 and suffix == NULL into a new helper
virNumaGetHugePageInfoDir which will only be called when a directory
path is expected to be returned. This solves the issue where the helper
was called with page_size == 0 expecting a file path in return, but
instead got a directory path and failed in virFileReadAll with:

    error : virFileReadAll:1358 : Failed to read file
                '/sys/devices/system/node/node0/hugepages/': Is a directory

Since virNumaGetPages API expects to return a directory by passing
page_size == 0 and suffix == NULL, it will now call the new helper.
Callers to virNumaGetHugePageInfoPath expect to return a file path
which could then be used in the call to virFileReadAll.

Signed-off-by: Luyao Huang <lhuang@redhat.com>