unittests: some fixes to fib_sr tests

[miri64]

This does not fix #4513, but it makes debugging it a lot easier by correcting the usage of embunit: an assert inside a helper function will cause the helper function to return but not finish the test, leading to very confusing outputs. This minimizes the output of the errors given in #4513 to only one error and I was able to give the analysis I gave there. Additionally, this fixes a lot of the broken formatting in the tests.

[OlegHahm]

ProTip: append ?w=0 to the URL for an easier review.

[miri64]

What does it do?

[cgundogan]

git diff --help
       -w, --ignore-all-space
           Ignore whitespace when comparing lines. This ignores differences even if one line has whitespace where the other line has none.

and it makes no difference if you use ?w=0 or ?w=1. I personally prefer ?w=1

[cgundogan]

changes are sane. Without this patch the fib_sr unittest fails because of a wrong usage of embunit. With this patch, the unittest still fails, but unrelated to the changes given here. ACK

[cgundogan]

and GO

[cgundogan]

@authmillenon, reminder: please backport