Update Python constants references to '_constants.py'
Update Python constants references to '_constants.py'

Update Python constants 'ADMINST_{DOWN,UP,OFFLINE}' to take their
values from the Haskell generated module 'lib/_constants.py'.

Signed-off-by: Jose A. Lopes <0fb9c4f8511df4ec2ae28af879e9d462f6218a2c@google.com>
Reviewed-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>

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