Makefile mod to adapt to e2c environment

Signed-off-by: balaskoa <Jeno.Balasko@ericsson.com>
Change-Id: I32b3783902b221ecc89e722900a189f308f494b0

Makefile.cfg

@@ -98,7 +98,9 @@ LTTNGUSTLOGGER := no
 
 # Path of the Java Developement Kit installation
 # (must be at least version  1.5.0_10)
+ifndef JDKDIR
 JDKDIR := /usr/lib/jvm/default-java
+endif
 
 # Path of OpenSSL installation: (always required)
 OPENSSL_DIR := default