Fix logcollector multi-line

[bah07]

Fixes the feature to group with the option multi-line in logcollector.

With configuration:

  <localfile>
    <log_format>multi-line:3</log_format>
    <location>/logcollector/test.log</location>
  </localfile>

The log receive nexts lines:

Test line 1
Test line 2
Test line 3
Test line 4
Test line 5
Test line 6
Test line 7

Logcollector generate the output:

(ag-ubu16) any->/logcollector/test.log Test line 1 Test line 2 Test line 3
(ag-ubu16) any->/logcollector/test.log Test line 4 Test line 5 Test line 6

[vikman90]

Please consider using strncmp() to check that the string starts with "multi-line:".