add upgrade test

[sg2342]

• this regression test reproduces Application hot upgrade failed erlang/rebar3#2558
• the test will succeed when keep attributes when stripping beams #906 is applied and fail otherwise
• while there make shelltest/run_test.sh also work on platforms where sed(1) is of the BSD/MacOS variant (BSD/MacOS sed does not work with a bare -i flag and GNU sed does not work with -i '' so using a backup for the in-place edit and remove it afterwards is the least painful solution that works for both)