SERVER-14027 renameCollection don't pass full spec to deleteObjects

If a collection being renamed has an index spec object which contains
a field prefixed by a dollar sign, deleteObjects will refuse to remove
the old spec object.  Uniquely identify the index in system.indexes by
{ns: ..., name: ...}.
SERVER-14027 Test renaming collection containing wildcard text index

(cherry picked from commit 969e42a89697d0cdfbb7e615f07d94745982b607)
Merge remote-tracking branch 'upstream/v2.6' into v2.6