doc: missing osd prefix to ioprio config options

http://tracker.ceph.com/issues/9676 Fixes: #9676

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
(cherry picked from commit 62235688c417ed19a472bc8a94bba005e03afbc6)
common: do not set ioprio if pid is not set

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
(cherry picked from commit c7e4c0bfe70bf29d3b8fe4df4e4b934853e33d26)
common: set_ioprio debug message including pid

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
(cherry picked from commit 33339c7754875eb7e513345ee6b26a9b2b4d2707)
osd: log error if set_ioprio fails to parse class

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
(cherry picked from commit 5088e0d49332d579ba7e33c2c9baee3d5f701a3e)
common: ceph_ioprio_string_to_class always returns -EINVAL

The l string is always empty because std::transform needs a
pre-allocated string. Replace with the in-place version. Add unit tests.

http://tracker.ceph.com/issues/9677 Fixes: #9677

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
(cherry picked from commit 3535b7aba3df8b54fa5117b8a9c2f52b8f0f118b)
Merge pull request #2661 from dachary/wip-9677-ioprio-class-giant

common: ceph_ioprio_string_to_class always returns -EINVAL