LU-11880 build: allow Debian build on Raspbian

LU-11880 build: allow Debian build on Raspbian

Allow the Debian build to work on Raspbian and other Debian and
Ubuntu variants that use the same build machinery.  Add armhf
to the list of allowed CPU architectures.

Lustre-change: https://review.whamcloud.com/34085
Lustre-commit: 7f3977ccd45fce0d150196e515286603135e7f3d

Test-Parameters: trivial clientdistro=ubuntu1804 testlist=sanity
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Iedc90ad32754f81a3d387a66409f07aaa305a5b1
Reviewed-by: Thomas Stibor <t.stibor@gsi.de>
Reviewed-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/34456
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>