Clarify default setting of 'metavg'
Clarify default setting of 'metavg'

This fixes issue 810, suggesting to clarify where the
default for 'metavg' comes from.

Signed-off-by: Helga Velroyen <2d0126b1ec6f9ec5cbec4a7012aa14faeaef10f5@google.com>
Reviewed-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>

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