Run tests with C locales.

This fixes tests failing on translated messages.
groups: searches also within localized names (RhBug:1150474)
base: package_upgrade does not reinstall or downgrade (RhBug:1149972)
base: package_downgrade prints message on failure
base: package_install allows install different arch of installed package
base: package_reinstall works only with the same package versions
doc: swap command alternative mentioned (RhBug:1110780)
fixed error summary traceback (RhBug:1151740)
tests: removed mock patch for _, P_