Document the generic query function
Document the generic query function

The way the generic query works was not documented anywhere. For
greater readability, add a short explanation to the genericQuery
function.

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

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