AURORA-565: update top level README with instructions on bootstrapping and running initial test

Updates README with basic instructions to get started with Apache Aurora.

Preview: https://github.com/jfarrell/incubator-aurora/tree/AURORA-565

Bugs closed: AURORA-565

Reviewed at https://reviews.apache.org/r/23317/
Improve aurora "job diff" command.

Add a new diff method, which uses field-by-field comparison of JSON trees for comparing running job configurations to potentially updated configs.

- Allow exclusion of semantically irrelevant fields.
- Provide a clearer list of the differences between configs.
- Provide a scripting-friendly alternative JSON syntax for diffs.

The old diff behavior is still available under the "--use-shell-diff" option.

Testing Done:
New unit tests of the JSON tree diff code, plus a bunch of new "job diff" tests of the new functionality.
All tests pass.

Bugs closed: aurora-520

Reviewed at https://reviews.apache.org/r/22457/
Revert "Improve aurora "job diff" command."

This reverts commit 92799eae2819cb81eba89ba6201f1ca333cfd503.

(Tests failed in CIB after passing locally.)
AURORA-583: Upgrade to public release of pants

Point pants at the public release instead of github fork.  Upgrades pex to
0.5.9 while we're at it.

Testing Done:
./pants src/test/python/apache/aurora:all -v

Bugs closed: AURORA-583

Reviewed at https://reviews.apache.org/r/23528/
Improve aurora "job diff" command.

Add a new diff method, which uses field-by-field comparison of JSON trees for comparing running job configurations to potentially updated configs.

- Allow exclusion of semantically irrelevant fields.
- Provide a clearer list of the differences between configs.
- Provide a scripting-friendly alternative JSON syntax for diffs.

The old diff behavior is still available under the "--use-shell-diff" option.

Bugs closed: aurora-520

Reviewed at https://reviews.apache.org/r/22457/
Revert "Improve aurora "job diff" command."

This reverts commit 2bb6342ec4ad2b62c2d6aab9621a79451e13ee29.
Improve aurora "job diff" command.

Add a new diff method, which uses field-by-field comparison of JSON trees for comparing running job configurations to potentially updated configs.

- Allow exclusion of semantically irrelevant fields.
- Provide a clearer list of the differences between configs.
- Provide a scripting-friendly alternative JSON syntax for diffs.

The old diff behavior is still available under the "--use-shell-diff" option.

Bugs closed: aurora-520

Reviewed at https://reviews.apache.org/r/22457/
Modify failing test.
Revert "Modify failing test."

This reverts commit 303a84f871620b541188442a2cbe324d338af919.
Revert "Improve aurora "job diff" command."

This reverts commit 83a99364bb60f75c7acfbcd33e57b8c3dc6d4319.
Fix logic error causing new slave attributes to be discarded.

Bugs closed: AURORA-582

Reviewed at https://reviews.apache.org/r/23653/
Move aurora commons version to 0.3.1.
Add argparse dep.