Print the bash command that caused the test to fail

Includes the `$BASH_COMMAND` and exit status that caused the test failure in the pretty failure output

Example:
```
~/p/bats(failure-context)$ bin/bats test/fixtures/bats/failing_and_passing.bats
1..2
not ok 1 a failing test
# /Users/rsouza/p/bats/test/fixtures/bats/failing_and_passing.bats:2
#   false exited with status 1
ok 2 a passing test
```