slapgrid: Support [manager:x] sections

In slapos:manager_list it is possible to enable list of managers, but as they
have to be configurable support sections for each manager by [manager:x]

So having configuration file like:

[slapos]
manager_list = mgr

[manager:mgr]
key = value

Will allow for the mgr manager to read values from manager:mgr

slapos/grid/slapgrid.py

@@ -208,6 +208,12 @@ def merged_options(args, configp):
             "reload_config_cmd",
             "slapos node restart firewall")
 
+  key = 'manager:'
+  options[key] = {}
+  for section in configp.sections():
+    if section.startswith(key):
+      manager = section[len(key):]
+      options[key][manager] = dict(configp.items(section))
   return options