proc: selftests: shotgun testing of read/readdir/readlink/write

proc: selftests: shotgun testing of read/readdir/readlink/write

Perform reads with nearly everything in /proc, and some writing as well.

Hopefully memleak checkers and KASAN will find something.

[[email protected]: /proc/kmsg can and will block if read under root]
Link: http://lkml.kernel.org/r/20180316232147.GA20146@avx2
Signed-off-by: Alexey Dobriyan <[email protected]>
[[email protected]: /proc/sysrq-trigger lives on the ground floor]
Link: http://lkml.kernel.org/r/20180317164911.GA3445@avx2
Link: http://lkml.kernel.org/r/20180315201251.GA12396@avx2
Signed-off-by: Alexey Dobriyan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>