unify testdata to only one dir

[thinkerou]

Unify test data to one dir: testdata.

[menghanl]

Thanks for this PR. We definitely want this.
A problem here is that, you need to run those tests or binaries in certain directory, otherwise they cannot find the testdata.

Our proposal is:

1. Add a go package testdata here
2. Add an exported function to testdata package (testdata.Directory()?), which returns the absolute path of the testdata directory. This function should look similar to the abs function we already have.
3. In all the places test files are needed, specify them using the newly added function.
   For example: var caFile = testdata.Directory() + "ca.pem"

What do you think?
If you agree, do you mind changing this PR to implement it?

[dfawley]

Add an exported function to testdata package (testdata.Directory()?)

Nit/bikeshedding: how about Path()?

For example: var caFile = testdata.Directory() + "ca.pem"

Note: prefer filepath.Join() to manual concatenation for cross-platform compatibility.

[thinkerou]

OK, I prefer testdata.Path("testdata/ca.pem") to testdata.Directory, but I not sure that we should use testdata.Path("ca.pem") or testdata.Path("testdata/ca.pem").

So, the PR have changed the follow points:

• Deleted two functions abs and goPackagePath in benchmark/worker/util.go file.
• Add new file testdata.go.
• Deleted some ca.pem,server1.pem and server1.key.
• Used new function testdata.Path().

[menghanl]

Thanks for the PR.
LGTM.