Changed hardcoded user home directory from '/opt/msm' to '$msm_dir'

When installing with to a non-standard directory, errors are thrown due to user being created with a home directory that doesn't exist. Fix sets user home directory to $msm_dir instead of '/opt/msm'.
Merge pull request #224 from Akythius/patch-1

Changed hardcoded user home directory from '/opt/msm' to '$msm_dir'