smbd: Separate aio_pthread indicator from normal EINTR

According to Posix and the Linux open(2) manpage, the open-syscall can
return EINTR. If that happens, core smbd saw this as an indication
that aio_pthread's open function was doing its job. With a real EINTR
without aio_pthread this meant we ended up in a server_exit after 20
seconds, because there was nobody to do the retry.

EINTR is mapped to NT_STATUS_RETRY. Handle this by just retrying after
a second.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=14285
Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Thu Feb 20 22:14:25 UTC 2020 on sn-devel-184

(cherry picked from commit aebe427b)
32 jobs for vl/4.11-14285 in 61 minutes (queued for 5 seconds)
Status Name Job ID Coverage
  Build
passed centos7-samba-o3 #445846472
docker shared

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passed ctdb #445846430
docker shared

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passed debian9-samba-o3 #445846460
docker shared

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passed fedora29-samba-o3 #445846478
docker shared

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passed fedora30-samba-o3 #445846482
docker shared

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passed opensuse150-samba-o3 #445846463
docker shared

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passed opensuse151-samba-o3 #445846469
docker shared

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passed others #445846409
docker shared

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passed samba #445846410
docker shared

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passed samba-ad-dc-1 #445846449
docker samba-ci-private

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passed samba-ad-dc-2 #445846419
docker shared

00:56:04

passed samba-ad-dc-3 #445846420
docker shared

00:44:25

passed samba-ad-dc-4 #445846422
docker shared

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passed samba-ad-dc-5 #445846424
docker shared

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passed samba-ad-dc-6 #445846426
docker shared

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passed samba-ad-dc-backup #445846433
docker samba-ci-private

00:42:01

passed samba-ad-dc-ntvfs #445846432
docker shared

00:46:05

passed samba-ad-member #445846418
docker shared

00:29:06

passed samba-ctdb #445846431
docker shared

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passed samba-fileserver #445846444
docker samba-ci-private

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passed samba-ktest-heimdal #445846447
docker samba-ci-private

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passed samba-libs #445846427
docker shared

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passed samba-none-env #445846411
docker shared

01:00:59

passed samba-nopython #445846412
docker shared

00:33:48

passed samba-nopython-py2 #445846414
docker shared

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passed samba-nt4 #445846451
docker samba-ci-private

00:45:50

passed samba-schemaupgrade #445846453
docker samba-ci-private

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passed samba-static #445846429
docker shared

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passed samba-systemkrb5 #445846416
docker shared

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passed samba-xc #445846417
docker shared

00:12:32

passed ubuntu1604-samba-o3 #445846457
docker shared

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passed ubuntu1804-samba-o3 #445846455
docker shared

00:35:15