monitoring: don't generate monitoring_id if given
monitoring: don't generate monitoring_id if given

only generate a monitoring_id if one isn't given in the config file.

this enables us to use the aToken/agentA fixture account.

cp16net/virgo-base,AlphaStaxLLC/rackspace-monitoring-agent,christopherjwang/rackspace-monitoring-agent,virgo-agent-toolkit/rackspace-monitoring-agent,cp16net/virgo-base,cp16net/virgo-base,AlphaStaxLLC/rackspace-monitoring-agent,kaustavha/rackspace-monitoring-agent,kaustavha/rackspace-monitoring-agent,virgo-agent-toolkit/rackspace-monitoring-agent,christopherjwang/rackspace-monitoring-agent,cp16net/virgo-base,cp16net/virgo-base