Prevent ssl key generation when disabled

The BMCWEB_INSECURE_DISABLE_SSL option was provided in CMakeLists.txt
but not used anywhere. Look at it when determining whether to
enable crow SSL (CROW_ENABLE_SSL).

Testing: Verified default image still compiles and verified
when BMCWEB_INSECURE_DISABLE_SSL is set to ON, bmcweb can
be put behind nginx and respond to redfish commands.

Change-Id: Ic1c2cf52df99923706bffac9553e258542b0ff7d
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index a932ef9..b55b7c3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -143,7 +143,9 @@
     add_definitions (-DCROW_ENABLE_DEBUG)
 endif (CMAKE_BUILD_TYPE MATCHES Debug)
 
-add_definitions(-DCROW_ENABLE_SSL)
+if (NOT "${BMCWEB_INSECURE_DISABLE_SSL}")
+    add_definitions(-DCROW_ENABLE_SSL)
+endif (NOT "${BMCWEB_INSECURE_DISABLE_SSL}")
 include_directories(${CMAKE_CURRENT_SOURCE_DIR}/crow/include)
 
 # Zlib