[NEXUS-6790] Copy yum metadata to group in case of a single yum member

commit 733115040ee852a206e25fc8ed822c3d733cd9fb
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Tue Oct 21 19:09:31 2014 +0300

    [NEXUS-6790] Fix test about conccurent running of MergeMetadataTask

commit 23886a203b7860cc04280dd5d68a00af474b4a23
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Tue Oct 21 18:59:04 2014 +0300

    [NEXUS-6790] Only copy when there is exactly one member

commit 3be3e20300823cfc6f22db89ab82282f33736665
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Tue Oct 21 18:19:34 2014 +0300

    [NEXUS-6790] Copy yum metadata to group in case of a single yum member