sdcm/cluster: fix get_nodetool_status (#1518)
sdcm/cluster: fix get_nodetool_status (#1518)

This patch fixed the split pattern of datacenter, currently all nodes status
will be wrongly merged into one datacenter. Ignored the spare title line
from result, and added the load unit to result.

@#### Expected return of example status:
{
   'datacenter2':{
      '172.17.0.3':{
         'load':'456.53KB',  <<<<<  load unit is added
         'tokens':'256',
         'state':'UN',
         'owns':'?',
         'host_id':'70d17de8-2839-4f30-829a-504d1a06176f',
         'rack':'rack1'
      }
   },
   'datacenter1':{
      '172.17.0.2':{
         'load':'456.53KB',
         'tokens':'256',
         'state':'UN',
         'owns':'?',
         'host_id':'70d17de8-2839-4f30-829a-504d1a06176f',
         'rack':'rack1'
      }
   }
}

@#### Actually return of example status:
{
   'Datacenter: datacenter1':{    <<<<<< wrong datacenter name
      '172.17.0.2':{
         'load':'456.53',
         'tokens':'256',
         'state':'UN',
         'owns':'?',
         'host_id':'70d17de8-2839-4f30-829a-504d1a06176f',
         'rack':'rack1'
      },
      '172.17.0.3':{
         'load':'456.53',
         'tokens':'256',
         'state':'UN',
         'owns':'?',
         'host_id':'70d17de8-2839-4f30-829a-504d1a06176f',
         'rack':'rack1'
      },
      'Address':{                   <<<<< spare title line
         'load':'Load Tokens',
         'tokens':'Owns',
         'state':'--',
         'owns':'Host',
         'host_id':'ID',
         'rack':'Rack'
      }
   }
}

Example status:

"""
Datacenter: datacenter1
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address     Load       Tokens       Owns    Host ID                               Rack
UN  172.17.0.2  456.53 KB  256          ?       70d17de8-2839-4f30-829a-504d1a06176f  rack1

Datacenter: datacenter2
=======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
--  Address     Load       Tokens       Owns    Host ID                               Rack
UN  172.17.0.3  456.53 KB  256          ?       70d17de8-2839-4f30-829a-504d1a06176f  rack1

Note: Non-system keyspaces don't have the same replication settings, effective ownership information is meaningless
"""
scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-longevity-tests