If Automake version > 1.11, force serial tests
If Automake version > 1.11, force serial tests

This fixes broken compilation on Debian Jessie (#802).
See also http://stackoverflow.com/questions/15820844/

Thanks to Apollon Oikonomopoulos for finding the solution
and Klaus Aehlig for helping to do it conditionally.

Signed-off-by: Petr Pudlak <9d19625f8ee825a2c398462ed335cbcf98f79c32@google.com>
Reviewed-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>

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