testsuite: add test for '.' correctly parsed in param's value

testsuite: add test for '.' correctly parsed in param's value

In kcmdline it's possible to have a dot in the param's value. The
support for this was added in 66f3228 ("libkmod: Add support for '.' in
module parameter on kcmdline") and is needed to correctly support some
modules that depend on it.

This test was added in order to make sure the commit  aa87854
("libkmod-config: Only match dot before '=' in /proc/cmdline") didn't
break it. Although that commit  message says it's allowing to match a
dot before '=' it's actually enforcing the first part of the string to
be always in the format "<module-name>.param". Dots after '=' are still
correctly allowed.