Do not run cpack at CMake time it is not available.

cpack was used to get the list of available i.e. ACTIVE CPack generators
in the CMake tests suite. This was done in order to get dynamically
available CPack generators like DEB or RPM that may or may not be
available on some platform like MacOSX depending on the fact that
some command are installed or not. We may do that but not during
initial configuration.
The current patch fixes the problem and we may do better in the future
like configuring CPack tests later.

Tests/CMakeLists.txt

@@ -717,31 +717,21 @@ ${CMake_BINARY_DIR}/bin/cmake -DVERSION=master -P ${CMake_SOURCE_DIR}/Utilities/
   ENDIF(CTEST_RUN_CPackComponents)
 
   IF(CTEST_RUN_CPackComponentsForAll)
-    # Analyze 'cpack --help' output for list of available generators:
-    execute_process(COMMAND ${CMAKE_CPACK_COMMAND} --help
-      RESULT_VARIABLE result
-      OUTPUT_VARIABLE stdout
-      ERROR_VARIABLE stderr)
-
-    string(REPLACE ";" "\\;" stdout "${stdout}")
-    string(REPLACE "\n" "E;" stdout "${stdout}")
-
-    set(collecting 0)
-    set(ACTIVE_CPACK_GENERATORS)
-    foreach(eline ${stdout})
-      string(REGEX REPLACE "^(.*)E$" "\\1" line "${eline}")
-      if(collecting AND NOT line STREQUAL "")
-        string(REGEX REPLACE "^  ([^ ]+) += (.*)$" "\\1" gen "${line}")
-        string(REGEX REPLACE "^  ([^ ]+) += (.*)$" "\\2" doc "${line}")
-        list(APPEND ACTIVE_CPACK_GENERATORS ${gen})
-      endif()
-      if(line STREQUAL "Generators")
-        set(collecting 1)
-      endif()
-    endforeach()
+    # Check whether if rpmbuild command is found
+    # before adding RPM tests
+    find_program(RPMBUILD_EXECUTABLE NAMES rpmbuild)
+    if(RPMBUILD_EXECUTABLE)
+      list(APPEND ACTIVE_CPACK_GENERATORS RPM)
+    endif(RPMBUILD_EXECUTABLE)
+    # Check whether if dpkg command is found
+    # before adding DEB tests
+    find_program(DPKG_EXECUTABLE NAMES dpkg)
+    if(DPKG_EXECUTABLE)
+      list(APPEND ACTIVE_CPACK_GENERATORS DEB)
+    endif(DPKG_EXECUTABLE)
+
     # ACTIVE_CPACK_GENERATORS variable
     # now contains the list of 'active generators'
-
     set(CPackComponentsForAll_EXTRA_OPTIONS)
     set(CPackRun_CPackCommand "-DCPackCommand=${CMAKE_CPACK_COMMAND}")
     # set up list of CPack generators