Enable running disk-image-create on SUSE Linux

- Ensures /sbin and friends are in $PATH when invoked (without this,
  various sudo invocations fail in exciting ways).
- Use dib-run-parts in lib/common-functions instead of run-parts
  (neither SLES nor openSUSE ship run-parts).
- Ensure dib-run-parts doesn't descend into subdirectories (same
  behaviour as run-parts).
- Move dib-run-parts from root.d to bin (cleaner, consistent with
  other elements with separate bin scripts).
- Tested by building Ubuntu image on openSUSE 12.3.
- Note: this doesn't add support for creating SUSE images, it just
  lets you run disk-image-create on SUSE-based distros.

Change-Id: I906c6bc3cf51cdf2c4415adeae1ca250faac25e1
Ensure $TMP_BUILD_DIR is actually created.

Previously if mktemp failed in function mk_build_dir, die was not
called.  The check for the exit code was actually checking that the
previous export statement completed successfully, not the call to
mktemp.

Change-Id: I477a2ce75c87c8167883ce7aa342e93c40770e29
Merge "Enable running disk-image-create on SUSE Linux"
Merge "Ensure $TMP_BUILD_DIR is actually created."
Add a new break on error

A user running di-b several times while developing an element may not
want to drop to a shell in all cases but may only want to do so if one
of their in target hooks failed.

This patch gives them the ability to do so, If break=after-error is set
then a user will be provided a in target shell taking over from where the
last failed command left off.

Change-Id: Ia2f7ac4c21b64b971f87f4ae9cb867981b13eb5e
Package with pbr.

Uses pbr-0.5.20 glob support to install elements, lib and scripts.

Change-Id: Ie466e753f6e75a943ced1a2939c9bb27aec4a6b0
Improve caching documentation.

It was a little weak, and folk need enough detail to reason about
performance.

Change-Id: I67f81ab5a206b3d42dd1e4e1eb52af88ac1a3adc
Merge branch 'master' into dev-yum
Capture the repositories from source-repositories.

We try to expose metadata to users about what dib included in the
image and source-repositories was not doing that, so this fixes it. It
also permits easy introspection from other elements (such as an
upcoming PyPI cache layer).

Change-Id: I1e48e65f69ebe1f4556cc3bf35ccf195e99bcc76
Merge branch 'master' into dev-yum