Fix#119
when parallel build is enable, multiple dpkg-buildpackage
instances are running at the same time. /var/lib/dpkg is shared
by all instances and the /var/lib/dpkg/updates could be corrupted
and cause the build failure.
the fix is to use overlay fs to mount separate /var/lib/dpkg
for each dpkg-buildpackage instance so that they are not affecting
each other.
Signed-off-by: Guohan Lu <lguohan@gmail.com>
