COMP: update find_package for boost

Modules/ThirdParty/Boost/otb-module-init.cmake

 # Required
 message(STATUS "Looking for required Boost headers")
-find_package ( Boost
-  1.35.0
-  REQUIRED
-  )
 
+# Mandatory components
+# - date_time -> ossim plugins
+set(OTB_Boost_COMPONENTS date_time)
 # Optional components
 # Boost (OPTIONAL_COMPONENTS does not work with Boost find_package)
 # unit_test_framework component is used only in GdalAdapters module
 if (BUILD_TESTING)
-  set(OTB_Boost_OPTIONAL_COMPONENTS unit_test_framework)
-  message(STATUS "Looking for optional Boost components : ${OTB_Boost_OPTIONAL_COMPONENTS}")
-  find_package ( Boost
-    QUIET
-    1.35.0
-    COMPONENTS ${OTB_Boost_OPTIONAL_COMPONENTS}
-    )
+  list(APPEND OTB_Boost_COMPONENTS unit_test_framework)
 endif()
+
+#Quiet find package to avoid message "Could not find boost" because unit_testing_framework is not installed
+#message(STATUS "Looking for optional Boost components : ${OTB_Boost_OPTIONAL_COMPONENTS}")
+find_package ( Boost
+  REQUIRED
+  1.35.0
+  COMPONENTS ${OTB_Boost_COMPONENTS}
+  )