pbuilder-deps: Use $ROOTDIR env var instead of hardcoding path

Change-Id: I9a24b15d0e814a211788cf4620e754d18ed846f8
diff --git a/pbuilder-hooks/D05deps b/pbuilder-hooks/D05deps
index 3e02eb2..9f35697 100755
--- a/pbuilder-hooks/D05deps
+++ b/pbuilder-hooks/D05deps
@@ -3,8 +3,8 @@
 echo "deb [trusted=yes] file://$DEPSBASE ./" >> /etc/apt/sources.list
 echo "deb [arch=amd64] http://storage.googleapis.com/bazel-apt stable jdk1.8" >> /etc/apt/sources.list
 echo 'Debug::pkgProblemResolver true;' > /etc/apt/apt.conf
-cp -r /rootdir/build/lintian /usr/share/
-cat /rootdir/build/bazel-release.pub.gpg | apt-key add -
-cat /rootdir/packages/mendel-keyring/cloud-key.gpg | apt-key add -
-cat /rootdir/packages/mendel-keyring/linux_signing_key.pub |apt-key add -
+cp -r ${ROOTDIR}/build/lintian /usr/share/
+cat ${ROOTDIR}/build/bazel-release.pub.gpg | apt-key add -
+cat ${ROOTDIR}/packages/mendel-keyring/cloud-key.gpg | apt-key add -
+cat ${ROOTDIR}/packages/mendel-keyring/linux_signing_key.pub |apt-key add -
 apt-get update