Fix type of 'node_whitelist' request parameter
Fix type of 'node_whitelist' request parameter

If opportunistic_locking is used, then 'node_whitelist' parameter passed
to the allocator is set to the LU's owned node locks. However, LU owned_locks
has type of 'set' while IReqInstanceAlloc expects type of
'ht.TMaybeListOf(ht.TNonEmptyString)'.

Signed-off-by: Christos Stavrakakis <ed3d4273a454573f57efbbf1dd7779fd0b08c549@grnet.gr>
Signed-off-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>
Reviewed-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>

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