Drop shebangs from bug_report and test scripts

At least `[[ ]]` and arrays are not Posix shell compatible.
And anyway it is better to run the scripts by default using
the current SHELL.

The only exception is `test/runner` that uses bash by default,
as it is normally used via make that uses /bin/sh otherwise.
Fix RUBY_ROOT in bug_report.sh
Fix auto-switching tests

The correct variable is RUBY_ROOT, not RUBY. It seemed to be renamed
during the development of auto-switching functionality.
Merge pull request #87 from tmatilai/bug_report

Fix RUBY_ROOT in bug_report.sh
Merge pull request #88 from tmatilai/fix-auto-tests

Fix auto-switching tests
Merge pull request #84 from tmatilai/non-posix-sh

Use bash in scripts and tests
If $PS1 isn't set, re-run the $SHELL in interactive/login mode.