Swap "ubuntu-debootstrap" for just "ubuntu"

See https://github.com/docker-library/official-images/pull/982#issuecomment-133207587.

Signed-off-by: Andrew "Tianon" Page <admwiggin@gmail.com>
(cherry picked from commit a5eec723f8)

contrib/builder/deb/ubuntu-precise/Dockerfile

@@ -2,7 +2,7 @@
 # THIS FILE IS AUTOGENERATED; SEE "contrib/builder/deb/generate.sh"!
 #
 
-FROM ubuntu-debootstrap:precise
+FROM ubuntu:precise
 
 RUN apt-get update && apt-get install -y bash-completion  build-essential curl ca-certificates debhelper  git libapparmor-dev  libsqlite3-dev --no-install-recommends && rm -rf /var/lib/apt/lists/*
 

contrib/builder/deb/ubuntu-trusty/Dockerfile

@@ -2,7 +2,7 @@
 # THIS FILE IS AUTOGENERATED; SEE "contrib/builder/deb/generate.sh"!
 #
 
-FROM ubuntu-debootstrap:wily
+FROM ubuntu:trusty
 
 RUN apt-get update && apt-get install -y bash-completion btrfs-tools build-essential curl ca-certificates debhelper dh-systemd git libapparmor-dev libdevmapper-dev libsqlite3-dev --no-install-recommends && rm -rf /var/lib/apt/lists/*
 

contrib/builder/deb/ubuntu-vivid/Dockerfile

@@ -2,7 +2,7 @@
 # THIS FILE IS AUTOGENERATED; SEE "contrib/builder/deb/generate.sh"!
 #
 
-FROM ubuntu-debootstrap:vivid
+FROM ubuntu:vivid
 
 RUN apt-get update && apt-get install -y bash-completion btrfs-tools build-essential curl ca-certificates debhelper dh-systemd git libapparmor-dev libdevmapper-dev libsqlite3-dev --no-install-recommends && rm -rf /var/lib/apt/lists/*
 

contrib/builder/deb/ubuntu-wily/Dockerfile

@@ -2,7 +2,7 @@
 # THIS FILE IS AUTOGENERATED; SEE "contrib/builder/deb/generate.sh"!
 #
 
-FROM ubuntu-debootstrap:trusty
+FROM ubuntu:wily
 
 RUN apt-get update && apt-get install -y bash-completion btrfs-tools build-essential curl ca-certificates debhelper dh-systemd git libapparmor-dev libdevmapper-dev libsqlite3-dev --no-install-recommends && rm -rf /var/lib/apt/lists/*