Changes in commit v3.4.0-rc1~124^2~1 (cmFindProgramCommand: Re-implement
search using more flexible approach, 2015-09-01) did not preserve the
behavior of looking for the given name with no search path at all.
Fix this and add a test case covering finding an absolute path with
no search directories.
Previously this command was tested only implicitly as part of larger
tests. Add a RunCMake.find_program test to cover find_program cases
specifically and independently.