Role classes wrapper for misc::package-pbuilder

Introduce role::package::pbuilder which simply call
misc::package-pbuilder and suitable for production.  I have adjusted the
system::role provided by misc::package-pbuilder to hint folks that this
class is deprecated

For labs introduce role::package::pbuilder::labs which needs a LVM
partition mounted at /mnt by role::labs::lvm::mnt. The reason is that
EQIAD instances have /var mounted on a filled up 2GB partition which
causes cowbuilder to bails out with not enough disk space.  Using the
huge /mnt would provide enough disk space.

Since the role::labs::lvm::mnt can be included elsewhere, I am not
redefining it there forcing people to avoid duplicate definitions.

Change-Id: Ia058a4ee5fd81403136d98fa4ab87b2b659353af