build CHANGE simplify libnetconf2 cmake search module

Use standard cmake modules for getting information about functionality
provided by the compiled library.
diff --git a/FindLibNETCONF2.cmake b/FindLibNETCONF2.cmake
index 824c0b6..d0e9580 100644
--- a/FindLibNETCONF2.cmake
+++ b/FindLibNETCONF2.cmake
@@ -4,8 +4,8 @@
 #  LIBNETCONF2_FOUND - system has LibNETCONF2
 #  LIBNETCONF2_INCLUDE_DIRS - the LibNETCONF2 include directory
 #  LIBNETCONF2_LIBRARIES - Link these to use LibNETCONF2
-#  LIBNETCONF2_ENABLE_SSH - LibNETCONF2 was compiled with SSH support
-#  LIBNETCONF2_ENABLE_TLS - LibNETCONF2 was compiled with TLS support
+#  LIBNETCONF2_ENABLED_SSH - LibNETCONF2 was compiled with SSH support
+#  LIBNETCONF2_ENABLED_TLS - LibNETCONF2 was compiled with TLS support
 #
 #  Author Michal Vasko <mvasko@cesnet.cz>
 #  Copyright (c) 2015 CESNET, z.s.p.o.
@@ -34,6 +34,8 @@
 #  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #
 
+INCLUDE(CheckSymbolExists)
+
 if (LIBNETCONF2_LIBRARIES AND LIBNETCONF2_INCLUDE_DIRS)
   # in cache already
   set(LIBNETCONF2_FOUND TRUE)
@@ -71,19 +73,8 @@
   if (LIBNETCONF2_INCLUDE_DIR AND LIBNETCONF2_LIBRARY)
     set(LIBNETCONF2_FOUND TRUE)
     # check compile flags
-    execute_process(COMMAND grep ENABLE_SSH ${LIBNETCONF2_INCLUDE_DIR}/nc_client.h RESULT_VARIABLE RETURN OUTPUT_QUIET ERROR_QUIET)
-    if (RETURN EQUAL 0)
-        set(LIBNETCONF2_ENABLE_SSH TRUE)
-    else (RETURN EQUAL 0)
-        set(LIBNETCONF2_ENABLE_SSH FALSE)
-    endif (RETURN EQUAL 0)
-
-    execute_process(COMMAND grep ENABLE_TLS ${LIBNETCONF2_INCLUDE_DIR}/nc_client.h RESULT_VARIABLE RETURN OUTPUT_QUIET ERROR_QUIET)
-    if (RETURN EQUAL 0)
-        set(LIBNETCONF2_ENABLE_TLS TRUE)
-    else (RETURN EQUAL 0)
-        set(LIBNETCONF2_ENABLE_TLS FALSE)
-    endif (RETURN EQUAL 0)
+    check_symbol_exists("NC_ENABLED_SSH" "nc_client.h" LIBNETCONF2_ENABLED_SSH)
+    check_symbol_exists("NC_ENABLED_TLS" "nc_client.h" LIBNETCONF2_ENABLED_TLS)
   else (LIBNETCONF2_INCLUDE_DIR AND LIBNETCONF2_LIBRARY)
     set(LIBNETCONF2_FOUND FALSE)
   endif (LIBNETCONF2_INCLUDE_DIR AND LIBNETCONF2_LIBRARY)