Specify DEFAULT section for libvirt_inject_partition

The first parameter of iniset is the section.

Fixes Ic71baa25cda4b65c79c7c5f64bbb802774e489f4

Change-Id: I5b31084aa9752ac568da94c6ed80ce2ab2befd68
Merge "Specify DEFAULT section for libvirt_inject_partition" into stable/havana