dist/debian: use ~root as HOME to place .pbuilderrc
dist/debian: use ~root as HOME to place .pbuilderrc

When 'always_set_home' is specified on /etc/sudoers pbuilder won't read
.pbuilderrc from current user home directory, and we don't have a way to change
the behavor from sudo command parameter.

So let's use ~root/.pbuilderrc and switch to HOME=/root when sudo executed,
this can work both environment which does specified always_set_home and doesn't
specified.

Fixes #3366

Signed-off-by: Takuya ASADA <4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>
Message-Id: <1523926024-3937-1-git-send-email-4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>

scylladb/scylla,avikivity/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,duarten/scylla,scylladb/scylla