Add API calls for multigroups

[mgmacias95]

Hi team,

This PR adds the following:

• Parameter replace in PUT/agents/:agent_id/group/:group_id:
  • With replace parameter it replaces current agent group by group_id.
  • By default, it creates a multigroup with current agent group and group_id.
• API call DELETE/agents/:agent_id/group/:group_id which removes group group_id from current agent's multigroup (or sets it to default if it belongs to a single one).

Example:

# curl -u foo:bar "localhost:55000/agents/groups?pretty"
{
   "error": 0,
   "data": {
      "totalItems": 2,
      "items": [
         {
            "count": 1,
            "mergedSum": "f1a9e24e02ba4cc5ea80a9d3feb3bb9a",
            "configSum": "ab73af41699f13fdd81903b5f23d8d00",
            "name": "default"
         },
         {
            "count": 0,
            "mergedSum": "0361f2c015a0fc2e6e7331789fd1cfee",
            "configSum": "ab73af41699f13fdd81903b5f23d8d00",
            "name": "dmz"
         }
      ]
   }
}
# curl -u foo:bar -XPUT "localhost:55000/agents/001/group/dmz?pretty&replace"
{
   "error": 0,
   "data": "Group 'dmz' set to agent '001'."
}
# curl -u foo:bar "localhost:55000/agents/groups?pretty"
{
   "error": 0,
   "data": {
      "totalItems": 2,
      "items": [
         {
            "count": 0,
            "mergedSum": "f1a9e24e02ba4cc5ea80a9d3feb3bb9a",
            "configSum": "ab73af41699f13fdd81903b5f23d8d00",
            "name": "default"
         },
         {
            "count": 1,
            "mergedSum": "0361f2c015a0fc2e6e7331789fd1cfee",
            "configSum": "ab73af41699f13fdd81903b5f23d8d00",
            "name": "dmz"
         }
      ]
   }
}
# curl -u foo:bar -XPUT "localhost:55000/agents/001/group/default?pretty"
{
   "error": 0,
   "data": "Group 'default' added to agent '001'."
}
# curl -u foo:bar "localhost:55000/agents/groups?pretty"
{
   "error": 0,
   "data": {
      "totalItems": 2,
      "items": [
         {
            "count": 1,
            "mergedSum": "f1a9e24e02ba4cc5ea80a9d3feb3bb9a",
            "configSum": "ab73af41699f13fdd81903b5f23d8d00",
            "name": "default"
         },
         {
            "count": 1,
            "mergedSum": "0361f2c015a0fc2e6e7331789fd1cfee",
            "configSum": "ab73af41699f13fdd81903b5f23d8d00",
            "name": "dmz"
         }
      ]
   }
}
# curl -u foo:bar -XDELETE "localhost:55000/agents/001/group/dmz?pretty"
{
   "error": 0,
   "data": "Group 'dmz' unset for agent '001'."
}
# curl -u foo:bar "localhost:55000/agents/groups?pretty"
{
   "error": 0,
   "data": {
      "totalItems": 2,
      "items": [
         {
            "count": 1,
            "mergedSum": "f1a9e24e02ba4cc5ea80a9d3feb3bb9a",
            "configSum": "ab73af41699f13fdd81903b5f23d8d00",
            "name": "default"
         },
         {
            "count": 0,
            "mergedSum": "0361f2c015a0fc2e6e7331789fd1cfee",
            "configSum": "ab73af41699f13fdd81903b5f23d8d00",
            "name": "dmz"
         }
      ]
   }
}

Best regards,
Marta