[rubygems/rubygems] Reset tmp directories before spec suite

If you abort running test suite with a quick double Ctrl-C, tmp files
will be left around, and they will interfere with the next test run.

To avoid this, make sure to clear them once at the beginning of the test
suite.

### Before

```
$ bin/parallel_rspec
16 processes for 175 specs, ~ 11 specs per process
.............................................................................................^C^C

Finished in 19.45 seconds (files took 0.42722 seconds to load)
94 examples, 0 failures

(... turbo tests backtrace ...)

$ bin/parallel_rspec
16 processes for 175 specs, ~ 11 specs per process
.F....F....F...F......^C

Failures:

(... failures' details ...)
```

### After

```
$ bin/parallel_rspec
16 processes for 175 specs, ~ 11 specs per process
.................................................................................^C^C

Finished in 18.18 seconds (files took 0.4383 seconds to load)
82 examples, 0 failures

(... turbo tests backtrace ...)

$ bin/parallel_rspec
16 processes for 175 specs, ~ 11 specs per process
................................................................................^C^C

Finished in 8.79 seconds (files took 0.45187 seconds to load)
80 examples, 0 failures

(... turbo tests backtrace ...)
```

https://github.com/rubygems/rubygems/commit/6767a52711

0 files changed, 0 insertions, 0 deletions