LU-14937 build: re-use config cache in 'make rpms/debs'

LU-14937 build: re-use config cache in 'make rpms/debs'

Idea is to pass along the value of the -C or --cache-file options from
the initial ./configure to the one launched as part of the rpm or deb
build.
But all the environment variables related cache info must be removed
otherwise the config cache file cannot be reused.

Lustre-change: https://review.whamcloud.com/44659
Lustre-commit: a5084c2f2ec851fe888838fb1e90aff8b5ed6fd2

Test-Parameters: trivial
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Iab4ae2815961ba10132d9cb44f82ca58d313e908
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/46197
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>