Build hangs when trying to checkout git submodules with absolute path

Summary

Build is hanging when git submodules is used with absolute path on OSX.
SSH process keeps stuck even after the build is successfully stopped.

Environment

• OSX macOS Sierra 10.12.6 (16G1114)
• Git 2.14.3 (Apple Git-98)
• Bamboo local agent

Steps to Reproduce

1. Create a repository with submodule configured with absolute path
   Example:

   [submodule "subrepo"]
     path = subrepo
     url = ssh://git@<IP>:<PORT>/repo/subrepo.git

2. Create an SSH key and make sure the public side is added to both git main repository and its submodule
3. Create a shared credential for that SSH key
4. Create a linked repository in Bamboo using the SSH URL of the main repository and set the Advanced options >> Use submodules
5. Configure a plan to use the linked repository and chekcout the code

Expected Results

1. Bamboo is able to checkout the code
   or
2. Build fails with a reasonable error informing the user what was wrong and no SSH process is left running

Actual Results

The build hangs, if we try to manually stop the biuld it stops but the SSH process keeps consuming a high amount of the CPU. If we try multiple builds we get more SSH processes stuck compromising the server performance.