Move assertions to beginning of ExecBlock
Move assertions to beginning of ExecBlock

Usually we aim for operations to succeed or not do
anything at all. Do the same when failing for internal
errors (like bugs in the locks requesting code).

Signed-off-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>
Reviewed-by: Niklas Hambuechen <98215d3a72cb13cc9c9956528e50119ca7d1fb8b@google.com>

yiannist/ganeti,ganeti/ganeti,leshchevds/ganeti,andir/ganeti,andir/ganeti,apyrgio/ganeti,leshchevds/ganeti,grnet/snf-ganeti,apyrgio/ganeti,dimara/ganeti,onponomarev/ganeti,bitemyapp/ganeti,mbakke/ganeti,dimara/ganeti,mbakke/ganeti,yiannist/ganeti,andir/ganeti,onponomarev/ganeti,grnet/snf-ganeti,ganeti/ganeti,bitemyapp/ganeti,leshchevds/ganeti,yiannist/ganeti,mbakke/ganeti,ganeti/ganeti