[tests] Allow to execute tests on target

Originally it was supposed tests would be executed inside build dir.

Notice that env.py.in and env.sh.in have not been left unused after f79e5b1 - removing now.

Relates NEMO#520
[libcontentaction] mlite no more using mlocale

mlite library no more relies on mlocale library to localize desktop
entry name and no alternative mechanism to implement the functionality
behind CONTENTACTION_L10N_PATH environment variable is provided by mlite
at the moment -- removing the feature.  To make 'lca-tool --l10n' tests
pass without the possibility to use CONTENTACTION_L10N_PATH, absolute
paths are specified for the X-MeeGo-Translation-Catalog key.

mlite passes '-' as 'prefix' to QTranslator::load() -- renaming files.

mlite uses qtTrId() -- translation catalogs must be 'id based'.

Relates NEMO#520