Fix iohelper usage with streams opened for read

Fix iohelper usage with streams opened for read

In b2878ed860ceceec3cd6481424fed0b543b687cd we added the O_NOCTTY
flag when opening files in the stream code. Unfortunately a later
piece of code was comparing the flags == O_RDONLY, without masking
out the non-access mode flags. This broke the iohelper when used
with streams for read, since it caused us to attach the stream
output pipe to the stream input FD instead of output FD :-(

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>