Don't change the default attach-method

Don't change the default attach-method.  The one configured by the
libguestfs packager is supposed to be correct for all libguestfs
users, and making ad hoc changes to it is not advisable.

For more information, see:
https://bugzilla.redhat.com/show_bug.cgi?id=984409#c8

Fixes bug: 1220102
Change-Id: Ie7726c37dd579e2c95b6156a9ddfdff9e855af83
Merge "Don't change the default attach-method"