UBUNTU: [Debian] supply perf with appropriate prefix to ensure use of local config

UBUNTU: [Debian] supply perf with appropriate prefix to ensure use of local config

If we do not supply an installation prefix when we are building perf
it will assume it is designed to run relative to the builders HOME.
This means that as built on a buildd we will check for the system
configuration relative to the buildd users home rather than in /etc.
This implies a local user could use this to compromise other users _if_
there is a buildd user installed on the system and they have access to it.

CVE-2013-1060
BugLink: http://bugs.launchpad.net/bugs/1206200
Signed-off-by: Andy Whitcroft <apw@canonical.com>