Check if there are conflicts on master when running the build

- This is taken from
  https://github.com/alphagov/specialist-publisher/commit/9a097249c142c6e7146706dfd5fc0282c92f4886,
  as a thing discussed in tech lead standup that could be useful and
  passed to me to do via Jamie.
Merge pull request #106 from alphagov/jenkins_test_merge_result_of_branches

Check if there are conflicts on master when running the build
Update db/structure.sql

* No changes directly relevant to bouncer
* Has new `host_paths.canonical_path`
Remove path_hash from bouncer tests

* Was required when it was part of a UNIQUE index
* Following deploy of
  https://github.com/alphagov/transition/commit/1b8887ba4f5d9150edb24e6ce6b0fe6a918922d2
  is not required
* No longer need digest/sha1
Merge pull request #107 from alphagov/remove-path-hash-references

Remove path hash references
Tidy up comment referring to hash
Update db/structure.sql to remove path_hash columns

This is dumped from Transition's database in dev, as usual. That dump
also wanted to remove the following line, but I haven't included that
change in this commit:

SET lock_timeout = 0;
Merge pull request #108 from alphagov/update_db_structure_without_path_hash

Update db/structure.sql to remove path_hash columns
Merge pull request #109 from alphagov/remove-path-hash-references

Tidy up comment referring to hash