Use pipe fds in insert_source_no_interest test instead of stdin.

[detly]

Fixes #96 where this test would fail when stdin is closed (eg. by redirecting from /dev/null).

(I copied the lowest-common-denomimator from the ping sources, so it emulated the existing behaviour where we just used a raw fd, but maybe it's worth just using our own Ping source?)

[codecov[bot]]

Codecov Report

Merging #108 (59544ba) into master (1bb9a66) will increase coverage by 0.29%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #108      +/-   ##
==========================================
+ Coverage   88.92%   89.22%   +0.29%     
==========================================
  Files          17       17              
  Lines        1698     1698              
==========================================
+ Hits         1510     1515       +5     
+ Misses        188      183       -5     

Flag	Coverage Δ
macos-latest	88.71% <ø> (+0.35%)	:arrow_up:
ubuntu-latest	87.43% <ø> (+0.20%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/loop_logic.rs	89.78% <ø> (+0.85%)	:arrow_up:
src/sources/generic.rs	84.74% <0.00%> (+5.08%)	:arrow_up:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 1bb9a66...59544ba. Read the comment docs.

[elinorbgr]

Thanks!