Catch DeviceCreationError unhandled exceptions
Catch DeviceCreationError unhandled exceptions

_CreateBlockDevInner is called twice in TLReplaceDisks. While this
should be fixed, right now this leaves the DeviceCreationError exception
unhandled, which causes a problem due to the fact that this exception
was never supposed to be sent over the wire. For 2.7 we just catch the
exception and convert it to an OpExecError, but we should later do a
more proper cleanup.

This addresses Issue 472.

Signed-off-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>
Reviewed-by: Michele Tartara <05f7077a2c6cbbdc4af4ba42e3ef89a0df846179@google.com>

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