LU-12825 build: change lbuild to support MOFED 4.7

LU-12825 build: change lbuild to support MOFED 4.7

* Remove 'alternate' name in MOFED tar
* use MLNX_LIBS to download rpms

Test-Parameters: trivial

Lustre-change: https://review.whamcloud.com/36333
Lustre-commit: 279c26466bff37dd25fe26e4bb56a16a9a797870

Change-Id: Ia5a4f51455be836a7df4fa6b3e9eccc17cffef2c
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Nathaniel Clark <nclark@whamcloud.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/36344
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>