Fix active index's order

Message Controller's active index is not ordere correctly. Since we're
using K for sorting operation, it should be in the second position right
after the equality filters' indexes ('q'). This is necessary because
MongoDB sorts everything before applying range filters ('e', 'c.e') and
compound indexes are traversed in order. Without this patch, mongodb
would filter records and then sort them in memory w/o using the index.

Fixes bug: #1206517

Change-Id: I54ac464ce849f2dcde92a96090c27c489ea80e97