Consider adding some build/moodle-plugin-ci.phar basic tests

[stronk7]

All tests are performed with bin/moodle-plugin-ci and that's ok and cover 99% of uses.

But it's also possible to download moodle-plugin-ci.phar and use it on any moodle directory.

99.99% of times it will work the same than the binary... but there are cases where it may not. For example, in #68 I faced a problem about a configuration file (internal to the phar) not being loaded and leading to any codechecker execution using that phar to fail. Hopefully its fixed (workaround found).

But the point is that the problem was detected only by coincidence, because I was building the phar and decided to give it a try, there isn't anything (in make or CI checks) verifying anything using the phar.

We need to cover it, no matter they are trivial runs, but verify all them work.

That or, alternatively, we stop building the phar (although personally I find it useful, just put in in place and can run everything against any plugin (core or contrib).

Registered, to consider it. Ciao :-)