Add option in Bamboo for locking agent for the complete plan build.

Hi I have build plan setup in Bamboo as follows:

Stage 1:
Job: Clean History
Job: Clean Repository
Job: Clean Cache
Stage 2:
Job: Build and Test
Stage 3:
Job: Report Results

Now the same plan is run for multiple branches in the GIT repository. Since we have only single clean environment we have only single Agent running all jobs sequentially. But what I see is when multiple checkin happen the Stages across multiple branches get mixed up, thus resulting in the following run sequence where stages of one branch get mixed with stages of other branch.

Branch 1, executes Stage 1
Branch 2, executes Stage 1
Branch 1, executes Stage 2
Branch 2, executes Stage 2
Branch 1, executes Stage 3
Branch 2, executes Stage 3

With this work flow, the last job will definitely fail as it will never get a clean environment. Not sure if this is a bug, but I believe a build plan run should be atomic and isolated and is currently not the case.