Rearrange the protocol x implementation tests

There is a core chuck of testing that is repeated for {SSH,HTTP} x
{go-git,libgit2}, which is done by repeating a func value in different
contexts. Instead of mutating variables in the func's closure, it's a
bit clearer (and shorter) to pass them to a higher-order func.

Signed-off-by: Michael Bridgen <[email protected]>

Author: squaremo