Bug 1162422 - <oo-install> crash on move node

- Fix oo-install crash when moving a node between districts
yum-validator: use sub-man to set repo options

subscription-manager now supports repo-overrides, which allow setting
options on RHSM repos that take precedence over what's specified in
`/etc/yum.repos.d/redhat.repo`. This commit updates the repo config
modifying routine `CheckSources.set_save_repo_attr` so that it calls out
to `/usr/sbin/subscription-manager` with appropriate options to set the
desired configuration setting in the repo overrides.

This also adds `reconcile_rhsm_config.py`, which provides o-a-y-v with a
way to report or fix settings mismatched between the local `redhat.repo`
file and repo-override settings. This is enabled with the
`--reconcile-overrides|-e` option to `oo-admin-yum-validator`

Enterprise bug: 1162296
https://bugzilla.redhat.com/show_bug.cgi?id=1162296
Updated README, man page and cleaned up some comments & doctext
Merge pull request #493 from dobbymoodge/repo_override_fix

yum-validator: use subscription-manager to set repo options
<oo-install> always set conf_node_external_eth_dev for origin
Bug 1163338 - Improve command detection and error handling

https://bugzilla.redhat.com/show_bug.cgi?id=1163338

- explicity search /sbin and /usr/sbin when looking for utilities
- improve error handling around confirm_access
Merge pull request #492 from detiber/bz1162422

Bug 1162422 - <oo-install> crash on move node
Bug 1163036 - <oo-install> fix crash when moving districts

https://bugzilla.redhat.com/show_bug.cgi?id=1163036

- previously if only one district was defined and you tried to move
  the host district, the installer would crash.
Merge pull request #496 from detiber/bz1163036

Bug 1163036 - <oo-install> fix crash when moving districts
Merge pull request #495 from detiber/bz1163338

Bz1163338 <oo-install> - Improve command detection and error handling
installer: use $TMPDIR instead of hardcoded /tmp

Change some temporary paths to honour $TMPDIR instead of hardcoded
full path. This allows to invoke the installer with a custom tmpdir
location. Note that $TMPDIR is used (same value) in all hosts though.
Related to part 1 of:

Bug 1146694 - Minor updates to oo-install
Bug 1146694 <oo-install> - set TMPDIR for remote commands if set