Don't use /tmp in tests

Apparently on a mac, `getCanonicalPath` resolves `/tmp` to `/private/tmp`, causing
this test to fail. I've replaced the example with something semantically
equivalent for testing purposes, but it will actually succeed when building
on OSX.

Before:
```
Results :

Failed tests:   testRelativePathNothingInCommon(hudson.plugins.android_emulator.util.UtilsTest): expected:<../../../[]tmp/foo/bar/baz/> but was:<../../../[private/]tmp/foo/bar/baz/>

Tests run: 47, Failures: 1, Errors: 0, Skipped: 0
```

After:
```
Results :

Tests run: 47, Failures: 0, Errors: 0, Skipped: 0
```