Excluding the module test utilities (module/lib/test)
Added unit tests for some low hanging fruit:

 * Config - getLastUpdated
 * Docs - getModuleDocumentation & getModules
 * Removed unused ImageUtil.downScale and added tests for ImageUtil.convertToJPG
Added some unit tests for the content storage backends
Enable preview processing on Travis CI
Propagating tests exit code in Grunt
Removed 'excluding pp tests' in README.md
Add a note about etherpad-lite @ 1.2.91 in the README
Added a test that verifies previews can be reprocessed with a revision filter
Try to speed up previews build and reduce failures by:

 * Reduce timeouts
 * Purge all previews queues before each test
 * Installing etherpad package
Removed unused lingering compare code in the content API
PR follow-up

 * Purging all queues before truncating Content CF
 * seconrevision -1 rather than initial + 5
Added the excellent log-range.sh script by @mrvisser

The logs will now also contain a line before and after each containing
the title of the test.

The logs for a particular test can be grepped by doing:
```
./etc/scripts/log-range.sh '<test name>' '<test name>' tests.log
```
Requiring MQ in the previews tests
Merge pull request #749 from simong/pp-travis

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