Remove Exceptions.convertToRuntimeEx()

Remove Exceptions.convertToRuntimeEx()

The uses of Exceptions.convertToRuntimeEx() had two problems:
1. The cast from IOException to RuntimeException will
   fail because they are incompatible types;
2. They make it unclear that an exception is being thrown.

This change replaces their uses with direct throws of
RuntimeExceptions.

Change-Id: I3af60da2bdd3230c568744f747a5910d797073c8
Signed-off-by: Gary Wu <gary.i.wu@huawei.com>