LU-1627 build: Change lbuild to use https://github.com/zfsonlinux

LU-1627 build: Change lbuild to use https://github.com/zfsonlinux

lbuild fetches zfs/spl source using git@github.com:zfsonlinux which
requires a ssh keypair with git hub. If we change this to
https://github.com/zfsonlinux then we will not need local keys for
github as part of the builds.

The option to change the default by using SPLZFSGITREPO should be kept.

So change
git clone ${SPLZFSGITREPO:-"git@github.com:zfsonlinux"}/$pkg.git $pkg
to
git clone ${SPLZFSGITREPO:-"https://github.com/zfsonlinux"}/$pkg.git $pkg

Signed-off-by: Chris Gearing <chris@whamcloud.com>
Change-Id: I34c870b9aea98001115ff43291a6f95c5d268016
Reviewed-on: http://review.whamcloud.com/3387
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Joshua Kugler <joshua@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>