Refactor the end to end test for stripping file writing and reading

According to off-line discussion with zhz and xinwei, we need to implement an end to end test for stripping file support:

• Create an EC zone;
• Create a file in the zone;
• Write various typical sizes of content to the file, each size maybe a test method;
• Read the written content back;
• Compare the written content and read content to ensure it's good;

This jira aims to refactor the end to end test class(TestWriteReadStripedFile) in order to reuse them conveniently in the next test step for erasure encoding and recovering. Will open separate issue for it.