Slips cannot start because redis port selected with -m is already used by p2p

[jsvobo]

In matterhorn server, running with -m gives an error.
slips selects port 32772 to use for redis DB, but this port is already in use!

Expected behavior
A clear and concise description of what you expected to happen.

Branch
This is on my branch jsvobo/mlflow_new_model_testing, but I think this should be aplicable everywhere, since I did not touch this part of slips at all

Environment (please complete the following information):

• OS: Linux

** Recommendation **

• Why cannot slips -m randomly select port?
• or if there is error, catch in try block, try another port?