Pass the build-specific variables automatically into environment variables (like plan/global variables do)

Steps to reproduce:

1) create plan, script task:

echo $bamboo_buildResultKey
echo $bamboo_buildNumber

2) run the plan
3a) expected result (in the logs) is to see something like

PROJ-PLAN-JOB1-1
1

3b) while current behavior is:

(these environment variables are undefined, that's why we see empty logs)

Seems we pass the plan/global variables into the environment:

• https://bitbucket.org/atlassian/bamboo/annotate/949eea7f1933/components/bamboo-core/src/main/java/com/atlassian/bamboo/process/EnvironmentVariableAccessorImpl.java#line-80

But we don't do that for built-in variables like:

• ${bamboo.buildPlanName}
• ${bamboo.buildKey}
• ${bamboo.buildNumber}
• ${bamboo.buildResultKey}
• ${bamboo.buildTimeStamp}
• ${bamboo.repository.revision.number}
• ${bamboo.build.working.directory}
  etc...