util: Adjust error paths for virNumaSetPagePoolSize
    
    Commit id '1c24cfe9' added new checks and error messaes for failure
    scenarios. Let's adjust those error messages to after the call to
    virNumaGetHugePageInfoPath in order to provide a more specific error
    message depending on node and page_size
    
    After this patch:
     # virsh allocpages --pagesize 2047 --pagecount 1 --cellno 0
     error: operation failed: page size 2047 is not available on node 0
    
     # virsh allocpages --pagesize 2047 --pagecount 1
     error: operation failed: page size 2047 is not available
    
    Signed-off-by: Luyao Huang <lhuang@redhat.com>