apache: testing to-execute-file for mere presence is not enough

Permission to execute that file must be granted so as not to preclude
the happy case (also, hopefully, the respective "test" program
implementation is not naive about "uid=0 equals superprivileges" for
when the script is not owned by such user while there can be further
security domain constraints, such as a lack of "CAP_DAC_OVERRIDE"
on Linux [imposed, e.g., with SELinux]).

Signed-off-by: Jan Pokorný <jpokorny@redhat.com>