common,tests: replace _have_modules() with _have_module()

common,tests: replace _have_modules() with _have_module()

The helper functions _have_modules() and _have_driver() have similar
roles, but they take different number of arguments. The former takes
multiple module names and the latter takes single module name. To make
their usage consistent, modify _have_modules() to _have_module() to take
single argument. This improves readability by checking one module per
line.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>