Switch the Bitbucket Downloader to use a supported mechanism for specifying the access token

[zanchin]

Our original method of using the access token was silently deprecated by Bitbucket on 2016-02-05. Research revealed that they now only support the Bearer access_token header method.

Also added a test for the generated BB Downloader script.

[tizzo]

I'm still seeing failures - will follow up with more details.

[tizzo]

Ok, for future reference I was seeing the following output:

START: build-86f486af-1326-4e03-8f81-b031d43286ee-task-54b06de4f9400000
build-86f486af-1326-4e03-8f81-b031d43286ee-task-54b06de4f9400000:
$ mkdir -p /src
$ cd /src
$ mkdir -p /src
$ cd /src
$ wget -q -O - --header 'Authorization:Bearer [REDACTED]' https://bitbucket.org/tizzo/awesome-drupal-project/get/53718c062076.tar.gz
$ tar xzf - --strip-components=1

gzip: stdin: unexpected end of file
tar: Child returned status 1
tar: Error is not recoverable: exiting now
$ exit
END: build-86f486af-1326-4e03-8f81-b031d43286ee-task-54b06de4f9400000

This was actually the result of an iptables rule getting changed on my local environment that was breakaing all outgoing network connections from inside a container. Now that I know what's up I restarted my VM and found that your code was working the whole time. Thanks!