Add section about disk template removal
Add section about disk template removal

The section describes categories of tasks for removing the disk
templates from the instances and was assembled by looking through all
occurences of disk_template in the python code base.

Signed-off-by: Aaron Karper <99cc1031546340b2b8ced5fe338b5890677a56ca@google.com>
Reviewed-by: Michele Tartara <05f7077a2c6cbbdc4af4ba42e3ef89a0df846179@google.com>

apyrgio/ganeti,yiannist/ganeti,ganeti/ganeti,ganeti/ganeti,onponomarev/ganeti,ganeti-github-testing/ganeti-test-1,leshchevds/ganeti,andir/ganeti,yiannist/ganeti,grnet/snf-ganeti,andir/ganeti,ganeti/ganeti,andir/ganeti,dimara/ganeti,apyrgio/ganeti,grnet/snf-ganeti,mbakke/ganeti,leshchevds/ganeti,yiannist/ganeti,leshchevds/ganeti,bitemyapp/ganeti,mbakke/ganeti,dimara/ganeti,bitemyapp/ganeti,mbakke/ganeti,onponomarev/ganeti,ganeti-github-testing/ganeti-test-1