Better exception when files are unaccessible

In some cases the Hadoop filesystem API will throw NullPointerException when trying to access files that have moved.
We'd want to catch those and give a better error message.
```
Caused by: java.lang.NullPointerException
at org.apache.hadoop.fs.FileSystem.globStatus(FileSystem.java:1043)
at org.apache.hadoop.mapreduce.lib.input.FileInputFormat.listStatus(FileInputFormat.java:211)
at parquet.hadoop.ParquetInputFormat.listStatus(ParquetInputFormat.java:395)
at parquet.hadoop.ParquetInputFormat.getFooters(ParquetInputFormat.java:443)
at parquet.hadoop.ParquetInputFormat.getGlobalMetaData(ParquetInputFormat.java:467)
```

**Reporter**: [Julien Le Dem](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=julienledem) / @julienledem

_{**Note**: *This issue was originally created as [PARQUET-20](https://issues.apache.org/jira/browse/PARQUET-20). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}