(Maint) Fix mis-use of rvalue functions as statements

(Maint) Fix mis-use of rvalue functions as statements

Without this patch applied the spec tests are invalid because they call
rvalue functions as if they were statements.  This is a problem because
Puppet 2.7.x currently throws an exception if a rvalue function is
invoked as if it were a statement function.  This exception from Puppet
is causing tests to fail.

This patch fixes the problem by changing the tests to assign the return
value of the functions to a variable.  This fixes the problem by
invoking the functions properly.

Paired-with: Andrew Parker <andy@puppetlabs.com>