Partial updates for getting unit and functional tests to pass

- CopyBlobResult: Update code to verify headers are present before trying to read their values, to avoid "Undefined index" errors.
- TableService*Test: Replace call to Windows-only `com_create_guid` with our SDK `getGuid`
- BlobRestProxyTest: There seems to have been an update in the Blob service to hold on to deleted containers for a much longer time than before. This means that most blob tests will fail when rerun, unless you wait for over 5 minutes. By adding some salt to each name, the tests are more robust.