Prefer BeTrue(), BeFalse() to Equal() for booleans
Retrieve deps for subdirectories and only download

Previously, we were retrieving dependencies for subdirectories but for
an unknown reason `go get` would not retrieve dependencies required by
`_test.go` files in subdirectories. We're not actually using any such
dependencies currently that aren't already required by the files we are
testing, but I came across the issue when writing an provisional test.

Also, only download the dependencies but don't install them. This is
necessary to prevent the following errors when using the `./...`
wildcard in conjunction with `third_party.go`:

    » make
    [11:44:53]
    rm -rf third_party/pkg/*/github.com/alphagov/govuk_crawler_worker
    go run third_party.go get -t -v ./...
    go install: no install location for directory
    /Users/matt/govuk/govuk_crawler_worker/http_crawler outside GOPATH
    go install: no install location for directory
    /Users/matt/govuk/govuk_crawler_worker/queue outside GOPATH
    go install: no install location for directory
    /Users/matt/govuk/govuk_crawler_worker/ttl_hash_set outside GOPATH
    go install: no install location for directory
    /Users/matt/govuk/govuk_crawler_worker/util outside GOPATH
    exit status 1
    make: *** [deps] Error 1
Exit if the RabbitMQ channel closes

We currently exit if the RabbitMQ connection drops, the Crawler simply
logs a fatal error and exits.

This commit does the same for when the RabbitMQ channel (NB channel, not
connection) drops.

Given the nature of the work the Crawler does, this does not present an
issue and it will continue where it left off when restarted. With our
current configuration, the service will be automatically restarted
within 30 minutes if it fails.

If this happens too frequently, we may consider improving this. But
currently, I have not yet seen an example of the channel closing without
the connection dropping at the same time.
Merge pull request #75 from alphagov/76261684-amqp-channel-closure

[#76261684] Exit if the RabbitMQ channel closes