Rename Fillable fields to Indexed fields
Rename Fillable fields to Indexed fields

The naming used in the previous commits did not reflect the use of
the fields well, and clashed with the concept of fillable parameters.
Thus some renaming was done, with slight documentation improvements.

Signed-off-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>
Reviewed-by: Jose A. Lopes <0fb9c4f8511df4ec2ae28af879e9d462f6218a2c@google.com>

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