* Fix crashes when running spack install under nohup
Fixes#4919
For reasons that I do not entire understand, duplicate_stream() throws
an '[Errno 22] Invalid argument' exception when it tries to
`os.fdopen()` the duplicated file descriptor generated by
`os.dup(original.fileno())`. See spack/llnl/util/lang.py, line
394-ish.
This happens when run under `nohup`, which supposedly has hooked
`stdin` to `/dev/null`.
It seems like opening and using `devnull` on the `input_stream` in
this situation is a reasonable way to handle the problem.
* Be more specific about error being handled.
Only catch the specific error that happens when trying to dup
the stdin that nohup provides.
Catching e as a StandardErorr and then
`type(e).__name__` tells me that it's an OSError.
Printing e.errno tells me that it's 22
Double checking tells me that 22 is EINVAL.
Phew.
36496b9174