MT#9683 Explicitely set $PATH to have debootstrap available from /usr/sbin/debootstrap

Addressing:

| + debootstrap --variant=minbase --components=main,contrib,non-free --arch=amd64 --keyring=/var/cache/pbuilder/base-wheezy-amd64.cow/etc/apt/trusted.gpg --include=wget wheezy /tmp/tmp.vNw1CmR4B1 http://debian.sipwise.com/debian
| source/wrapper/piuparts_runner: line 54: debootstrap: command not found

wrapper/piuparts_runner

@@ -2,6 +2,8 @@
 
 set -x
 
+export PATH='/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin'
+
 rm -f piuparts.tap
 
 [ -d artifacts ] || { echo "Error: directory artifacts does not exist." >&2 ; exit 1 ; }