From aosp/1329396, the RBE metrics protobuf file is part of the
metrics uploading process. The RBE metrics protobuf file is
generated by running the bootstrap shutdown command. A new function
named DumpRBEMetrics was written in order to generate the RBE metrics
protobuf file before sending to the uploading process.
Bug: b/140638454
Test: * Unit test cases
* Ran RBE build on my local host and verified the
metrics protobuf file is created.
* Ran non-RBE build after RBE build and verified that
the previous metrics protobuf file was deleted.
Change-Id: I4b8068905cb67c4b8c2d94793917b98974fed707
62f1bf2378