Rocks sync users doesn't catch usermod errors

[zootboy]

I ran into a small issue when running "rocks sync users". The usermod command that it tries to execute fails if the user is logged in via ssh. This error is not caught, and the subsequent commands are executed as if it had succeeded.

core/src/rocks-pylib/rocks/commands/sync/users/plugin_fixnewusers.py

Line 179 in 21f1d39

for line in os.popen(cmd).readlines():

This resulted in a large number of duplicate entries in the /etc/auto.home file, as each failed sync attempt appended a new copy of the user's automount line.