@ret was not initialized when there was only one partial match.

Also, refactor the code to return all matching values.

Fixes: 3fd9bf9d7d9fc0290fd25f709b60a3a8f5c7e334

https://github.com/NetworkManager/NetworkManager/pull/123

Have less logic in TestNmcli.

The developer can re-generate .expected files with

 $ NM_TEST_REGENERATE=1 ./clients/tests/test-client.py

Note that these files are also dist-ed, so that the tests also work
from a source-tarball. For that, we need to add them to EXTRA_DIST.

Previously, this was done manually in the base Makefile.am file. This
was cumbersome, because when adding a new test, the developer would need
to manually add the files.

Now, let the test (with NM_TEST_REGENERATE=1) also generate a makefile
part.

This bug resulted in spurious lines with "--pretty --mode tabular",
whenever nmc_print() was called with multiple rows.

Currently, the only case where this was visible was with:

  $ nmcli --pretty general permissions

(note that "--mode tabular" is the default).

Fixes: 16299e5ac0a8882e13d42122278013b74bc6d34d

Before:

  $ nmcli c modify Dukkha ipv4.ignore no
  Error: invalid property 'ignore': 'ignore' is ambiguous (ignore-auto-routes x (null)).

After:

  $ nmcli c modify Dukkha ipv4.ignore no
  Error: invalid property 'ignore': 'ignore' is ambiguous (ignore-auto-routes x ignore-auto-dns).

call_nmcli_l() would test for 3 languages: 'C', 'de', and 'pl'. There
is no fundamental difference between 'de' and 'pl', so there is no need
to test for two languages.

We will use it, and it must be available anyway, because the stub server
also requires it.

It is a hook to set one or several D-Bus properties at once. Properties that are
to be set-able, have to be whitelisted in the stub.