virttest: Fix local filesystem test providers

According to the file URI scheme, files in a local
filesystem look like:

file:///etc/fstab

And not

file://etc/fstab

Also, fix the composition of paths for the test providers.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
virttest.bootstrap: Fix subtests.cfg creation

Correctly determine names of test provider by
looking at paths of config files and .py files.

This way, we can have a local test provider nearly
identical to an upstream test provider, with separate
test source files, allowing people to hack on
upstream test providers.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
virttest.standalone_test: Fix locating test source files

When a fixed test provider is a given, we can easily
restrict where to look for source files.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
test-providers/README: Give an example of filesystem URI

As it was lacking on the example file.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #1421 from autotest/fix-local-testproviders

Fix local testproviders