HTTPS upload tests skipped when not executed from uploaders directory

[nzhechev-bosch]

In setSSLCerts function in uploaders/common_test.go a relative path is used when setting the SSL_CERT_FILE environmental variable. Because of this, the value is not correct, unless the test is executed from the 'uploaders' directory - e.g. when executing all tests from the repo root directory with the go test ./... command - and the corresponding tests are skipped.

[nzhechev-bosch]

It turns out the problem is not the directory from which the tests are executed. The actual issue is #57.