Fix index hardcoding, potential name collisions with reserved words, and fix uninitialized variable access

[ngie]

Summary

Fix index hardcoding and potential name collisions with reserved words

• Rename nitems variable to num_items to avoid overshadowing nitems(..) macro
• Use nitems(..) instead of hardcoding indexes
• Change i/index from int to unsigned int type for consistency with other variables and to fix -Wsign-compare warnings
• Rename string to string_arr to make it clear that it's char**, not char*, and to also avoid potential issues with reserved keywords in languages (C/C++) or interfaces that might crop up in the future
• Fix uninitialized variable access that was causing a large degree of grief on stable/10 when I was running the tests as noted in https://reviews.freebsd.org/D4767 .

MFC after: 5 days
Sponsored by: EMC / Isilon Storage Division

Test Plan

• Built the change with both clang and gcc5 successfully on head.

% kyua test -k /usr/tests/lib/libnv/Kyuafile

[ngie]

lib/libnv/tests/nv_array_tests.cc

31 ↗

(On Diff #11895)

I need to restore this. For some odd reason sys/dnv.h isn't getting size_t from sys/param.h...

[oshogbo]

Some extra comments.

lib/libnv/tests/nv_array_tests.cc

120–124

num_items == nitems(string_arr) ?

236–237

num_items == nitems(number) ?

[ngie]

• Fix a few more hardcoded items by using nitems(..)
• Re-add sys/types.h for size_t in sys/dnv.h (it isn't needed on head, but it's definitely needed on stable/10 for some odd reason :(..)

[ngie]

Remove some variables that are accessed incorrectly (they're not initialized)

This fixes the tests when run on stable/10

[oshogbo]

Possibly we could change those few lines but outside that please commit it ASAP ;)

lib/libnv/tests/nv_array_tests.cc

64

i < nitems(testbool) ?

67

, nitems(testbool));

74

, nitems(testbool));

145

i < nitems(string_arr) or num_items

[ngie]

Committed as r293130, r293131, r293134, and r293135. Thank you for all the help Mariusz :)!!!