Check for python-yaml at configure time
Check for python-yaml at configure time

Signed-off-by: Bernardo Dal Seno <dcdd79c5479cb9d1329ec01d126f02cb045aa103@google.com>
Reviewed-by: Michele Tartara <05f7077a2c6cbbdc4af4ba42e3ef89a0df846179@google.com>

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