Fix crashes when running spack install under nohup (#4926)

* 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.

0 files changed, 0 insertions, 0 deletions