rhbz#1084067: Make sure the OVAL session is created before using it
rhbz#1084067: Make sure the OVAL session is created before using it

Addressing segfault:
 #0  oval_agent_eval_definition (ag_sess=0x0, id=0x7f0513727580 "oval:org.open-scap.cpe.rhel:def:6") at oval_agent.c:160
 #1  0x00007f0512638fb1 in _xccdf_policy_cpe_check_cb (sys=<value optimized out>, href=0x7f051367b6c0 "openscap-cpe-oval.xml",
     name=0x7f0513727580 "oval:org.open-scap.cpe.rhel:def:6", usr=<value optimized out>) at xccdf_policy.c:823
 #2  0x00007f0512616b54 in cpe_check_evaluate (item=<value optimized out>, cb=0x7f0512638f00 <_xccdf_policy_cpe_check_cb>, usr=0x7f0513670940) at cpedict.c:173
 #3  cpe_item_is_applicable (item=<value optimized out>, cb=0x7f0512638f00 <_xccdf_policy_cpe_check_cb>, usr=0x7f0513670940) at cpedict.c:183
 #4  0x00007f0512616c0c in cpe_name_applicable_dict (cpe=0x7f0513670800, dict=<value optimized out>, cb=0x7f0512638f00 <_xccdf_policy_cpe_check_cb>, usr=0x7f0513670940)
     at cpedict.c:157
 #5  0x00007f05126391af in xccdf_policy_model_platforms_are_applicable_dict (model=0x7f051366bb20, dict=0x7f0513676960, platforms=0x7f05136707a0) at xccdf_policy.c:880
 #6  0x00007f0512639322 in xccdf_policy_model_platforms_are_applicable (model=0x7f051366bb20, platforms=0x7f05136707a0) at xccdf_policy.c:972

Hexadorsimal/openscap,jan-cerny/openscap,mpreisler/openscap,Hexadorsimal/openscap,postfix/openscap,OpenSCAP/openscap,postfix/openscap,jan-cerny/openscap,openprivacy/openscap,postfix/openscap,Hexadorsimal/openscap,ybznek/openscap,redhatrises/openscap,isimluk/openscap,isimluk/openscap,OpenSCAP/openscap,ybznek/openscap,postfix/openscap,jan-cerny/openscap,OpenSCAP/openscap,postfix/openscap,isimluk/openscap,openprivacy/openscap,jan-cerny/openscap,redhatrises/openscap,ybznek/openscap,Hexadorsimal/openscap,redhatrises/openscap,Hexadorsimal/openscap,mpreisler/openscap,mpreisler/openscap,ybznek/openscap,jan-cerny/openscap,OpenSCAP/openscap,openprivacy/openscap,jan-cerny/openscap,ybznek/openscap,redhatrises/openscap,openprivacy/openscap,redhatrises/openscap,Hexadorsimal/openscap,isimluk/openscap,mpreisler/openscap,postfix/openscap,OpenSCAP/openscap,mpreisler/openscap,OpenSCAP/openscap,mpreisler/openscap,redhatrises/openscap,openprivacy/openscap,isimluk/openscap,ybznek/openscap,openprivacy/openscap,isimluk/openscap