Previously, all tools with run_automatically set to True were automatically

executed on every published review request. This has been broken since the

addition of tool profiles.
This change fixes automatic execution of tools and changes it such that when a

'review request published' signal is received, tools are automatically executed

only if a set of rules (specified as AutomaticRunGroups) are followed. An

AutomaticRunGroup is very similar to Review Board's DefaultReviewer - it is

basically a set of tool profiles which will be automatically executed when a

file in the diff matches the file regex specified.

Without any AutomaticRunGroups created, I published a review request with a

diff, and did not see a tool execution get created.
I then added some AutomaticRunGroups, and tried several cases where a tool

execution was not created (as expected):

- Published a new review request with no diff.

- Updated a review request's title (diff was not added).

- Published a review request in a repository that did not match any

  AutomaticRunGroup's repos.

- Published a review request with files that did not match any

  AutomaticRunGroup's file regexes.
I also tried publishing review requests where tool executions were created, and

reviews were posted by Review Bot:

- Matched an AutomaticRunGroup with a single profile.

- Matched an AutomaticRunGroup with multiple profiles.

- Matched several AutomaticRunGroups with overlapping sets of profiles, and saw

  that only unique tool profiles were executed.