The docker image that used during e2e test
composed of repo and tag flags that are
passed to the test itself.
The problem is that the docker image initialized
before the flags are parsed. Hence, it will always contains
the default flags value.
Moving the variable into a separate function, fixing the issue.
Also, moving the global variables to `e2e_test.go` since
it commonly used by all tests.
Signed-off-by: Talor Itzhak <titzhak@redhat.com>
